By Alex Rogers and Gregory Krieg, CNN

(CNN) -- The dog days of summer are usually a low-key time for members of Congress to be with their family and constituents back home. But this August 4, some are running for their political lives, challenged by insurgent candidates on the left and right.

Kansas, which hasn't sent a Democrat to the Senate in nearly 90 years, has suddenly become the center of the struggle between the two parties for control of the chamber. The Sunflower State also features another Republican primary race, between an indicted congressman and state official, that could affect the Democrats' chances of picking up a House seat in a Trump district.

Michigan Rep. Rashida Tlaib, a founding member of the "squad," is being challenged by one of her 2018 rivals, the moderate president of Detroit's city council. In Missouri, Rep. William Lacy Clay, a longtime incumbent, is defending his seat in a race with progressive activist Cori Bush, whom he defeated two years ago.

The Republican primary race to replace Michigan Rep. Justin Amash, the only Libertarian in the House, will test whether "Never Trumper" attacks hold sway in the rare district represented by one.

And Missouri holds a vote for a ballot initiative on whether to expand Medicaid, which advocates say would provide insurance to more than 230,000 additional people.

Here are six things to watch for in Tuesday's elections.

Will Kris Kobach succeed?

Democrats haven't won a Senate seat in Kansas since 1932, the longest losing streak for the party in the country. But the Republican establishment is terrified that spell might be broken if the state elects on Tuesday former Kansas Secretary of State Kris Kobach as its nominee.

Kobach's crusades to restrict illegal immigration and voting through stringent identification laws have made him a divisive figure, endearing him to conservatives but repulsing Democrats and some moderate Republicans. He lost the 2018 governor's race to Democrat Laura Kelly, who ran on overturning the budget-busting era of Republican Gov. Sam Brownback.

But two-term Republican Rep. Roger Marshall, who has the support of the man he's seeking to replace, Sen. Pat Roberts, and powerful groups like the Kansas Farm Bureau, Kansans for Life and the Chamber of Commerce, does not have the endorsement of the man who could potentially ensure him victory: President Donald Trump.

During the 2018 gubernatorial race, Trump gave Kobach a late boost in endorsing him a day before the Republican primary. (Kobach beat then-Gov. Jeff Colyer by only 343 votes and then lost to Kelly by 5 points.) But last week, Trump indicated to associates on Air Force One that he would not publicly intervene in the Kansas Senate race despite the urging of top Republicans.

That has left a fiercely competitive primary, where secretive political groups have spent way more than the candidates' campaigns.

A Democratic-aligned organization called the Sunflower State has spent over $4.6 million on ads boosting Kobach, while the Republican-affiliated group Plains PAC has spent over $3.3 million bashing him, according to the Kantar's Campaign Media Analysis Group. The Senate Leadership Fund, which is aligned with Senate Majority Leader Mitch McConnell, has also spent over $1.8 million supporting Marshall, a OB-GYN doctor. The Marshall campaign has spent about $1.5 million on ads while the Kobach campaign has spent about $250,000.

A wild card in the race is the campaign of plumber company owner Bob Hamilton, which has spent more than $2.5 million on advertising. In one of his latest ads, a man says that Hamilton is a "crazy, Trump-supporting, American-loving, flag-waving conservative." Hamilton is then shown water-skiing, holding the American flag.

"Kobach can't win," adds the man. "And Marshall? He's one hot mess, moderate squish."

The winner of the primary is expected to face Democratic state Sen. Barbara Bollier. A former Republican, she has broken state fundraising records by bringing in $7.8 million, according to the latest Federal Election Commission filings.

Indicted congressman runs for reelection

Rep. Steve Watkins, a Kansas Republican, is facing a primary challenge from Kansas State Treasurer Jake LaTurner. The congressman was recently charged with three felonies related to voter fraud, including providing false information, voting without being qualified and unlawful advance voting, as well as a misdemeanor charge of failing to notify the DMV of change of address. Watkins used a UPS store as his registration address for a 2019 municipal election in order to conceal the fact that he was then living with his parents, according to the Kansas City Star.

Watkins has said that the charges from the Shawnee County District Attorney's office are "hyper-political" and "very suspicious," asserting that he's "done nothing wrong" and would set "the record straight."

He has temporarily stepped down from his assignments on the House Foreign Affairs, Veterans' Affairs and Education and Labor committees. Afterward, House GOP Leader Kevin McCarthy vouched for the congressman and said that he still supports Watkins. But in the aftermath of the charges, LaTurner earned the endorsement of the Kansans for Life's PAC and Kansas Republican Rep. Ron Estes.

Watkins has endured other questions about his record. During his first congressional race in 2018, he ran as a political outsider and an Army veteran. But he exaggerated his role as a defense contractor in the Middle East, according to the Star.

LaTurner claims that Watkins will lose in November even though Trump won the district by 19 points in 2016. The Democrats' likely nominee is Topeka Mayor Michelle De La Isla.

In 2018, Trump and former Kansas Sen. Bob Dole backed Watkins, but he won by less than a point. The congressman was then named an honorary co-chairman of Trump's reelection campaign in Kansas along with other members of Congress, and Watkins has amplified his connections to Trump during the campaign.

Dennis Taylor, a Topeka attorney and former head of several state agencies, is also seeking the Republican nomination and was recently endorsed by the Star newspaper's editorial board.

The squad on defense in Michigan

Progressive congressional candidates have built on their successes from 2018 during this hectic primary season, defeating Democratic incumbents in Illinois and New York.

On Tuesday, though, they will be playing defense in Michigan's 13th district, where Rep. Rashida Tlaib is a facing challenge from one of the candidates she beat in a crowded primary two years ago, Detroit City Council President Brenda Jones.

Tlaib narrowly won the 2018 primary, a six-way contest, with less than a third of the vote. This time out, it is a head-to-head race and all of the other candidates from two years ago are backing Jones, who actually won, just ahead of Tlaib, a smaller concurrent contest that year to finish out the term preceding Tlaib's now-famous arrival on Capitol Hill.

But a lot has changed since the two were last on the ballot.

Tlaib and her "squad" mates are national political stars and have the financial backing that comes with it. She has also deepened her connections in the district and, during the worst of the coronavirus in Detroit, effectively turned her campaign apparatus into a tool for checking up and sending help to residents.

Jones entered the race relatively late, toward the end of March, and announced in early April that she tested positive for Covid-19. Her campaign, hobbled from the start, has struggled to raise money and only launched its first television ad last week.

The primary in Michigan comes a week before Minnesota's, where Rep. Ilhan Omar is also running her first race as an incumbent. Both Jones and Omar's opponents have accused the freshmen lawmakers of forsaking their home districts in pursuit of national profiles. That message fell flat in New York, when it was leveled against Rep. Alexandria Ocasio-Cortez in June, when she romped to victory over a bigger spending campaign than Jones'.

A progressive challenge in Missouri

After falling short in 2018, Cori Bush is challenging 10-term incumbent Rep. William Lacy Clay, in Missouri's 1st congressional district for a second time.

The Clay family has held the St. Louis seat since 1969, when former Rep. William Clay Sr., one of the founders of the Congressional Black Caucus, first entered Congress. His son, who is favored to fend off Bush again, won the nomination two years ago with nearly 57% of the vote -- a clear victory, but not strong enough to discourage Bush and her allies.

A registered nurse and ordained minister who became a leading activist in Ferguson, Bush is better known in the district and raised more money this time around. She has the backing of Sen. Bernie Sanders, who did not endorse in 2018, and Justice Democrats, the progressive group best known for backing insurgent leftist Democratic primary bids.

But Clay hasn't stood still since the last election. Last year, he co-sponsored the Green New Deal resolution written by Ocasio-Cortez (see his press release from the time, complete with a picture of them smiling together) and Massachusetts Sen. Ed Markey. He has also argued on the campaign trail that, with so much devastation and doubt amid the coronavirus pandemic, his experience in Congress should appeal anew to voters.

"These times in the middle of a global health pandemic, with a cratering economy and people crying out for economic and social, racial justice — now is not a time for amateur hour," Clay told the St. Louis Post-Dispatch last week.

Bush, in turn, has spoken about her own struggles -- "I am the people that I serve," she says -- and sought to cast Clay as a political fixture that needs changing.

"I'm running to serve the people of #MO01," Bush tweeted last week. "@LacyClayMO1 is running to protect his family's dynasty."

The Republican race to replace Justin Amash

Rep. Justin Amash, the Republican-turned Libertarian who briefly mulled a presidential campaign, will retire this year after five terms in office representing a district anchored by Grand Rapids, Michigan.

The Republican primary race to replace him includes Peter Meijer, an Iraq War veteran and former NGO conflict analyst in Afghanistan whose family founded the Meijer grocery store chain, and businesswoman and state Rep. Lynn Afendoulis.

Meijer, 32, is endorsed by McCarthy and the powerful DeVos family. But Afendoulis, who is backed by a number of state legislators and anti-abortion rights groups, has attacked Meijer, saying she is a stronger supporter of Trump.

While Meijer has said he's "not going to be a rubber stamp" of the president, he told a local ABC affiliate that they "align" on many issues, including "ending our wars overseas."

Jamie Roe, an adviser for Meijer's campaign, said that Afendoulis' attacks calling Meijer a Never Trumper are "ridiculous," saying Afendoulis had social media posts in 2016 that were critical of the President. Roe said that Meijer's opponents "have attacked him from day one" since he is the front runner. "They've all failed miserably to do it," he added.

Cooper Mohr, the Afendoulis campaign manager, told CNN, "Lynn's message of working with the President to bring Michigan back, standing up for life, and sending a real conservative to congress is why Lynn is going to win."

Meijer has raised over $1 million and loaned himself $475,000, more than any other candidate in the race, according to the latest FEC filings. Afendoulis's campaign has raised over $625,000 and loaned herself $256,000.

Democrat Hillary Scholten, an immigration attorney who served in the Department of Justice during the Obama administration, has raised over $1 million. But it'll be difficult for any Democrat to win the district that Trump won by nine points in 2016.

Missouri Medicaid expansion initiative

The Show-Me state will vote on Tuesday on whether to expand Medicaid a decade after the Affordable Care Act passed, potentially providing health care to hundreds of thousands of Missourians.

If it passed, Missouri would be the sixth state to approve Medicaid expansion by ballot initiative, following Maine, Utah, Nebraska, Idaho and Oklahoma. The advocates have coalesced an array of groups, including the state Chamber of Commerce, the state AFL-CIO, hospitals, health care professionals, the NAACP, and AARP, in favor of the measure. The initiative's supporters have raised over $10 million, while its opponents have raised much less.

But both sides are claiming they have the momentum ahead of the vote.

"This summer in Oklahoma, voters made access to expanded Medicaid a right that politicians can never take away by putting it in their state constitution. Now, Missouri has the chance to do the same," said Jonathan Schleifer, executive director of the Fairness Project, which supports Medicaid expansion ballots across the country. "Americans are tired of politicians abandoning their neighbors without health care -- particularly in the midst of a pandemic. Time and time again, voters have made it clear they want more affordable and accessible health care, and we expect that message to be heard loud and clear on election night."

The opposition is less well-funded. But Missouri Governor Mike Parson, Republican state legislators, the state Farm Bureau and anti-abortion groups have all vociferously led the charge against it. Parson moved the vote from November to the lower-turnout primary date in August, defending the decision from his critics in saying it was about "policy, not politics" to give more time to prepare for a potential "massive spending initiative" when the state faces a "major health, economic, and budget crisis" caused by the coronavirus pandemic. A study conducted by Washington University estimated that Missouri's Medicaid expansion would be "roughly revenue neutral."

Americans for Prosperity, the main political arm of the influential Koch network, claims to have invested "well into the six figures on mail, radio, and digital efforts," in addition to making "1 million contacts" to oppose the measure, according to spokesman Kevin Brinegar. He warned that the Medicaid expansion "will only result in higher taxes, cuts to essential services, and less quality health care for current Medicaid recipients."

"I think it's going to be close either way," said Tracy King, a consultant helping lead the opposition campaign. "I feel like the momentum is on our side. It's all going to depend on who shows up to vote."