Originally Published: 04 NOV 22 07:00 ET

Updated: 04 NOV 22 13:17 ET

By Maeve Reston, CNN

(CNN) -- Nowhere in the country has the struggle between election denialists and democracy defenders played out in more vivid detail than in Arizona, where Democratic Sen. Mark Kelly's ability to hold off late momentum from Trump-backed GOP nominee Blake Masters will be key to Democrats' hopes of defending their narrow Senate majority.

Now running for a full six-year term, Kelly -- a retired astronaut and the husband of former Rep. Gabby Giffords -- entered the race in an enviable position as a formidable fundraiser with a personal brand that lent him bipartisan appeal in Arizona, where a third of the electorate are independents.

But the economic headwinds facing Democrats, as well as President Joe Biden's low approval ratings, have complicated his political fortunes. Republicans need a net gain of just one seat to pick up control of the Senate on Tuesday, and Democrats are already on defense in Nevada, Georgia and New Hampshire.

Arizona has emerged as one of the most important battleground states in the nation -- not only for Senate and governor this year and likely the next presidential contest -- but also because it is the fulcrum of key demographic changes that are testing the reach of both parties.

The Grand Canyon state has also been the site of some of the most dramatic scenes in the fight over the future of democracy. Those include former President Donald Trump's attempts to pressure state officials to overturn the 2020 election results; the repeated partisan "audits" that ultimately reaffirmed Biden's win; and the alarming scenes late last month of masked, activists -- some of them armed -- turning up to monitor and film voters at ballot drop boxes in a quest to prevent widespread voter fraud (that has so far proved non-existent).

The contest between Kelly, who was elected in a 2020 special election to fill the seat of the late Republican Sen. John McCain, and Masters, a venture capitalist who won his primary after embracing Trump's lies about the 2020 election, has played out against that backdrop.

Though Masters is a political novice who struggled to raise money, he was bolstered by his former boss, Peter Thiel, in the primary, and has seen late assistance from Trump's super PAC and the political arm of the Club for Growth after the Senate Leadership Fund, the party's main super PAC, cut its spending here to divert resources elsewhere. And he has closely allied himself with Kari Lake, the telegenic former news anchor who is in a dead heat in the gubernatorial contest with Democratic Secretary of State Katie Hobbs and could help pull him across the finish line.

A Fox News poll released Tuesday showed no clear leader in the Senate contest, while a New York Times/Siena College poll released Monday gave Kelly the edge, 51% to 45% among likely voters.

Former President Barack Obama swooped into Arizona this week to campaign for Kelly and other Democrats, warning that "democracy as we know it may not survive in Arizona" if election deniers like Masters, Lake and GOP Secretary of State nominee Mark Finchem are elected on Tuesday.

Kelly has cast his opponent as an extremist who would jeopardize abortion rights, Social Security, Medicare and democracy itself -- characterizations that Masters rejects.

"Blake Masters has some beliefs that are just dangerous for Arizonans," Kelly said during the rally with Obama Wednesday night in Phoenix. "He is now questioning the results of an election that is still six days away. ... This is dangerous, folks."

But Republicans see the race differently, sensing a clear opportunity in a state that Biden won by less than 10,500 votes. Democrats like Kelly and Biden, Masters told a crowd in Mohave County earlier this week, have "made life in America, life in Arizona, more dangerous, less affordable."

Masters encouraged his crowd to be "the tip of the spear" and to go out and "manufacture this red wave" -- one the GOP hopes will help them gain control of the Senate, which is currently split 50-50 with Vice President Kamala Harris casting the tie-breaking vote.

Entering the general election phase of the campaign, Masters had appeared to be pivoting toward more moderate stances that would broaden his appeal -- removing some of his more extreme positions on abortion and the 2020 election from his campaign website and acknowledging during a debate with Kelly that he had not seen evidence of voter fraud that would have changed the outcome of the 2020 election.

But he reversed course after receiving a phone call from Trump urging him to "go stronger" on election denialism, a conversation that was captured in a Fox documentary.

"Look at Kari. Kari's winning with very little money. And if they say, 'How is your family?' she says the election was rigged and stolen. You'll lose if you go soft. You're going to lose that base," Trump told Masters in the call that occurred some time after the debate.

"I'm not going soft," Masters replied.

When asked this week what he would say to moderates who are frustrated by inflation, but also concerned about his statements about the 2020 election, Masters said he doesn't think those voters "are concerned about what I say about 2020."

"I think the most important things by far right now to voters are inflation, crime and the border," he told CNN's Kyung Lah in an interview. "I invite everybody, whether they're Republican, moderate or Democrats, to ask themselves, 'Am I better off now than I was just two years ago?'... In almost all cases, unfortunately, the answer is a resounding no."

"We've got a wide-open southern border -- moderates don't like that," Masters added. "We've got 13% inflation in Maricopa County -- moderates don't like that. Moderates also want to be able to walk around -- and be safe walking around," he said, pointing to the homicide rate in Phoenix. "So, you don't have to be a political partisan not to be okay with that."

Kelly has argued that he has shown his independence from the Biden administration in Washington, DC, seeking to distance himself from national Democrats on immigration in a border state.

During a debate last month, he said he had "stood up to Democrats when they're wrong on this issue ... including the president." He noted that he took a stand against the administration when it announced the intention to end Title 42, the pandemic-era policy that allowed border patrol agents to send migrants back to their home countries.

"When the president decided he was going to do something dumb on this, and change the rules," Kelly said during the debate, "I told him he was wrong."

While first lady Jill Biden is headed to Arizona, Kelly has not campaigned with Joe Biden.

On the trail this week with Obama -- whom Democrats have deployed to the battleground states where the current president's approval numbers are underwater -- Kelly played up his outsider credentials. He was introduced by his wife, who was seriously wounded in a mass shooting in 2011 and later became a prominent advocate for measures to prevent gun violence. He stressed that he had never intended to run for office before 2020 -- "that was always Gabby's job" -- but noted he had dedicated his life to public service and was committed to tackling Arizona's challenges ahead.

Obama tried to help Kelly burnish his independent credentials by highlighting his unique experience as a combat pilot turned US senator: "You know when they had the 'Top Gun' movie?" the former president said, "all those people in the movie -- those are actors; he is actually a top gun."

"There is so much at stake in this election in six days," Kelly said in his closing argument in Phoenix. "We all know guys like Blake Masters ... somebody who thinks they know better than everyone about everything. Letting them make decisions for you is dangerous. So in just six days, let's make sure that we beat him."