By Adam Levy and Ethan Cohen, CNN

(CNN) -- Florida and Arizona hold primaries on Tuesday, teeing up the House and Senate races that will be critical to the balance of power in Washington come November.

Democrats must hold on to Sen. Bill Nelson's seat in Florida and win in Arizona's Senate race in order to have a shot a taking the majority in the Senate.

In Arizona, a Republican Senate candidate's reaction to Sen. John McCain's ailing health caused a last-minute controversy. In Florida, the Senate contest is already set, but both parties will select their nominees for governor in what is expected to be a competitive race in November.

Oklahoma is also holding a runoff election to determine who will be the Republican gubernatorial nominee. Democrats are eyeing this race as a potential flip this year.

What we'll learn tonight

WILL MCCAIN'S PASSING CHANGE THE RACE? Former state Sen. Kelli Ward walked back comments late Monday about the timing of the McCain family announcing he was stopping medical treatment and a tweet saying political correctness is a cancer. She apologized but also said the media misinterpreted some of her comments. McCain, who represented Arizona in both houses of Congress for more than 30 years, wasn't exactly embraced by any of the candidates in the race -- Ward, GOP Rep. Martha McSally or former Maricopa County Sheriff Joe Arpaio.

They all ran towards President Donald Trump, in a sign of his hold over Republican voters. Ward was already lagging behind McSally, the establishment's favorite to defeat the likely Democratic nominee in the fall.

HAS TRUMP PERMANENTLY CHANGED THE GOP PRIMARY GAME? The President's endorsement of Rep. Ron DeSantis immediately affected the GOP contest to replace Gov. Rick Scott. DeSantis is riding the wave of the Trump endorsement with a smaller ground game than his top rival, state Agriculture Commissioner Adam Putnam. Most statewide races come down to strong outreach and heavy media buys in Florida's diverse areas and media markets, but Trump's nod of approval may change that for Republicans. His strong support from the northern panhandle through the Gulf Coast in the South could prove that a tweet is mightier than the door knock.

CAN PROGRESSIVE DEMS SURPRISE? Progressives Sen. Bernie Sanders (I-VT) and Alexandria Ocasio-Cortez, who defeated powerful New York Rep. Joe Crowley in a primary in June, have both supported underdogs in key Florida Democratic primaries. If either Tallahassee mayor Andrew Gillum or activist Michael Hepburn can beat their better-known opponents, it would be a boost to the progressive movement, but it also might hurt Democrat's chances of flipping a vulnerable governor's mansion and House seat. Tonight's Democratic winner and the margin of victory will say a lot about the left in Florida. A united Democratic Party in Florida is vital to break the almost two decades-long GOP rule in Tallahassee, and with at least seven Republican-held congressional districts at play to flip, control of Congress may hinge on it as well.

What to watch tonight

ARIZONA (polls close 10 p.m. ET)

Flake's retirement after just one term gives Democrats one of their best shots at picking up a Senate seat. The GOP establishment hopes McSally can hold off far-right candidates Ward and the controversial Arpaio. Trump has yet to endorse a candidate in the race, having positive things to say about all three of them. On the Democratic side, Sinema is expected to easily defeat attorney Deedra Abboud and is already campaigning for November. Republican Gov. Doug Ducey could also be vulnerable this fall. Since the six-day teachers strike this past spring, education has emerged as a key issue in the race. Democrat David Garcia, an Arizona State University professor, is focusing on his experience in the area, but he faces tough challengers from State Sen. Steve Farley and Kelly Fryer, the CEO of the YWCA Southern Arizona.

CNN views more than half of Arizona's congressional districts as in play this year, with the 2nd District vacated by McSally as the most likely to flip. Hillary Clinton won the district in 2016, giving a strong start to either former Rep. Ann Kirkpatrick or 2016 nominee Matt Heinz, who are locked in a tight race for the nomination. The winner will be an immediate target of Republicans looking to keep control of the House.

FLORIDA (all polls closed at 8 p.m. ET)

Nelson's seat is vital in the battle for Senate control; both he and GOP Gov. Rick Scott are expected to skate through the primary to the general. The big drama will be in the primaries to replace Scott. On the Republican side, DeSantis hopes an endorsement from Trump will outweigh Putnam's attacks on DeSantis as an out-of-touch creature of Washington. On the Democratic side, Former Rep. Gwen Graham and Philip Levine, the former mayor of Miami Beach, look to be the front runners for the Democratic nomination. Tallahassee Mayor Andrew Gillum could surprise Democrats here. Democrats think any of the three can win, pointing to the slim margin they lost by in 2014. In the House, keep an eye on the 27th District being vacated by retiring GOP Rep. Ileana Ros-Lehtinen. CNN rates the race Lean Democrat. In the Democratic primary, former HHS Secretary Donna Shalala faces tough challenges from State Rep. David Richardson and Michael Hepburn, a former academic adviser at the University of Miami. On the Republican side, the endorsement from the Miami Herald could propel former Doral councilwoman Bettina Rodriguez Aguilera, who claims to have been abducted by aliens, to a stronger-than expected finish as she and several other Republicans try to catch front-runner Maria Elvira Salazar, a former TV reporter. CNN ranks eight Florida races as vulnerable in November, only one of which is currently held by a Democrat.

OKLAHOMA (all polls closed at 8 p.m. ET)

Runoff primary races in Oklahoma don't normally get a lot of attention, but the Sooner State could be see a big victory for Democrats this year. Republican Gov. Mary Fallin's popularity has fallen dramatically in her final months in office, giving Democrats some optimism that former state Attorney General Drew Edmondson could be her replacement. Democrats describe Edmondson's time in office as 'someone who fights for the little guy.' Former Oklahoma City Mayor Mick Cornett and Tulsa businessman Kevin Stitt will face off in the Republican runoff Tuesday. Democrats admit Cornett's time in office in one of the state's biggest cities would put up a stronger fight in the fall. Stitt's business practices have come under scrutiny, giving Democrats hope should he prevail over the former mayor, they will have a strong chance to win.