TUCSON, Ariz. >> Sen. John McCain does not say much these days about Donald Trump’s attack on his five-plus years as a prisoner of war. Instead, he clenches his teeth and says he will support the Republican Party’s presumptive nominee, who once said derisively about the senator’s time in captivity, “I like people that weren’t captured.”

In the triple-digit swelter here in Arizona, his home state, McCain, who was the Republicans’ presidential nominee and standard-bearer in 2008, did not openly bemoan this moment from his long political life. He is focusing on what he considers his toughest re-election fight yet, and is betting that the only way to keep his seat is to support Trump.

“I’m fair game. I’m in the arena,” said McCain, 79, whose thinning face reflects the decades he has spent traveling around his massive and increasingly diverse state.

Still, the episode sits with traces of bitterness, like old coffee grounds at the bottom of his cup, even if he says otherwise.

For a moment, the July attack on McCain seemed to be Trump’s undoing. McCain said he recalled a recent chat with a World War II veteran who had been in a German prison camp. As he delivered the man a missing medal, “he said to me, ‘Why would Trump say something like that about us?’” the senator said. “Frankly, I didn’t have an answer for it.”

But Trump has since called for mass deportations of undocumented immigrants and a wall at the Mexican border, and now the billionaire businessman could be the force that ultimately topples the indomitable McCain. An estimated 433,000 Hispanics are expected to vote in Arizona in November, an 8 percent increase from 2012.

And McCain has a credible Democratic challenger, Rep. Ann Kirkpatrick, who grew up on an Indian reservation and has strong support from the state’s sizable Native American population. “I just came from a Latino round table, and they are really concerned about McCain’s support for Trump,” she said Tuesday. “It’s very personal here.”

She is working with the state’s Democrats to harness these forces against McCain and his old guard, which is largely behind Trump.

Kirkpatrick said that being anti-Trump “is a strong message,” but she acknowledged that “it’s not the only message.” She recently opened a field office in Tempe, and has many Arizona State University volunteers working the phones. Working out of an old bank, aides sit in the former vault (the door has been removed) to go over McCain’s statements, year by year, and look for inconsistencies that suggest too long a stay in Congress.

“The race comes down to whether Arizonans take a step back and judge John McCain for being John McCain and his remarkable life of public service,” said Grant Woods, a former state attorney general and the senator’s friend for decades. “And not as being a long-term incumbent, and not as a Republican in a year when the party has a controversial nominee. If they do that, he will win walking away. If they don’t, then it could be tight. Could he lose? Yeah.”

Despite the personal attacks by Trump on the senator’s integrity and war record, McCain cannot afford to reject Trump and alienate his many supporters in Arizona if he hopes to hold his seat, an agonizing trade-off. McCain is the embodiment of much that voters in both parties, but especially fans of Trump, have said they would like to jettison this year. He is the ultimate establishment player, having served in Congress for nearly four decades — five terms in the Senate alone.

“Back in the Middle Ages, I was known as the maverick,” McCain said, smiling wanly.

He is an unapologetic free trader, an interventionist abroad who continues to defend the deeply unpopular war in Iraq, a supporter of private industry and markets, and the original, if inconstant, champion of changes to the immigration system that would help some undocumented immigrants become citizens.

To succeed in what most people believe will be his last political campaign, McCain must canter around the state assuring Trump’s detractors that he does not share the businessman’s visions for mass deportation and the dissolution of NATO, while continuing to woo an angry Republican base that overwhelmingly voted for Trump in the state’s March primary.

“I’ve been feeling it out there for some time,” McCain said. “In the southern part of the state here, they are not feeling the recovery at all. Then there is this whole issue with these young people and kids carrying around all this debt.”

“That’s the Bernie effect,” he said, referring to Sen. Bernie Sanders’ youth appeal in the Democratic primaries.

He added, “The turmoil in this race is more than I’ve ever seen. Younger, newer voters are registering for only one reason, to vote against Trump. So my challenge is to convince that younger newer voter that I am for them.”

His greater challenge may be with Latinos angry at Trump. According to an analysis of voter and census data by the National Association of Latino Elected and Appointed Officials Educational Fund, Latinos are expected to account for 17 percent of Arizona’s registered electorate this year, with a voter turnout rate at close to 70 percent. Nearly 45 percent of Latino registered voters are Democrats, the report found.

McCain remains most at home with other veterans, like the one he visited — on Memorial Day, another man waiting on medals.

“His wife said he was staying alive to get those medals,” McCain said, smiling at the memory. “Sometimes it’s a nice job.”