On Monday night, McCain accepted the Liberty Medal and delivered an acceptance speech unlike any other. Without naming names, McCain warned American citizens of leaders who "rather find scapegoats than solve problems."
That's one hell of a right hook for an 81-year-old with brain cancer.
Reeling from the blow, Trump told radio talk show host Chris Plante, "people have to be careful because at some point, I fight back" and he promised it wouldn't be pretty.
McCain wiped his brow and shrugged it off.
"I've faced far greater challenges than this," he told reporters.
In fact, McCain has held his own for more than two years now even though Trump has the advantage in height, weight, reach, and age.
And remember, these guys are fighting for the same team, the Republicans, which makes the slugfest all the more epic. During his presidential run in 2008 against Barack Obama, McCain actually had Trump's support.
Trump told CNN's Wolf Blitzer that McCain is "a good man, I know him very well. He's a very smart guy. He's a tough guy. I think he'd be a great president."
Once Trump entered the political ring himself, things changed. Here's a blow-by-blow account:
Round One: The first hit came after Trump's now infamous statements in June 2015 about Mexicans being murderers and rapists. McCain, trying to save face with Arizona's growing Hispanic voter base, told The Arizona Republic that the comment was offensive.
But, let's not forget McCain is a true politician and didn't want to alienate the other growing voter base — angry, far-right Republicans. So, he sprinkled in a little freedom of speech caveat, adding, "but he's entitled to say what he wants to say."
Round Two: Right before candidate Trump's first Phoenix visit in July 2015. McCain, Senator Jeff Flake and Governor Doug Ducey declined the invitation.
This not-so-subtle diss did not go unnoticed by Trump, who then fired back and told the crowd, "If the right person runs against John McCain, he will lose." During the same speech, he told a crowd of 4,200 that the answer to illegal immigration was a giant border wall and that Mexico was going to pay for it.
In response, McCain said Trump was merely "firing up the crazies."
And then came the tweets.
The thousands of people that showed up for me in Phoenix were amazing Americans. @SenJohnMcCain called them "crazies"--must apologize!— Donald J. Trump (@realDonaldTrump) July 16, 2015
.@SenJohnMcCain should be defeated in the primaries. Graduated last in his class at Annapolis--dummy!— Donald J. Trump (@realDonaldTrump) July 16, 2015
Round Three: Trump fell into his natural role of playground bully and the insults started getting personal.
At a question-and-answer session in Iowa later that July, Trump claimed that McCain was not a war hero.
Taken aback, the event's moderator, pollster Frank Luntz, interjected, "He is a war hero." Trump cut him off and let loose yet another now infamous quote, "I like people that weren't captured, OK?"
Naturally, this ignited a firestorm. And naturally, Trump refused to apologize and still does to this day.
Round Four: The media continued to look to McCain after every of one of Trump's outlandish comments, from the "blood coming out of her wherever" in reference to journalist Megyn Kelly to false claims about McCain's own track record writing legislation to support veterans.
McCain continued to deflect the blows.
He started most interviews with "I can't comment on everything that goes on," pepper in a generalized statement about the American people being offended and then end with "But Mr. Trump is able to say whatever he wants to say in some ways."
McCain's opponent in the 2016 Senate race, Democratic front-runner Ann Kirkpatrick, used his silent support of Trump against him both in debates and in television ads.
Round Five: After Trump's big win on Super Tuesday in March 2016, McCain couldn't stay quiet anymore. In April, he announced he would not attend the Republican National Convention to see Trump accept the party's nomination.
Despite this, McCain remained party loyal. He told reporters he was a proud "Ronald Reagan-Teddy Roosevelt Republican" but he candidly told Arizona supporters that Trump was hurting the Republican brand.
In August, McCain seemed to be waving the white flag when he signed off on a formal endorsement of Trump.
Round Six: Then the Access Hollywood tape happened. You know this tape, the one where the current President of the United States brags about groping women. Or, more specifically, "grab 'em by the pussy."
McCain had had enough. He started punching back again. He withdrew his support and seemingly re-entered the ring to beat up Trump for another year.
Round Seven: The biggest showdown came this summer over health care reform.
McCain continued to keep us guessing as the Republican party weighed heavy on his back. The suspense around which way he would vote felt cinematic as he heroically returned to Washington after undergoing brain surgery.
News of McCain's aggressive brain cancer diagnosis had Trump changing his tune and even calling him a war hero.
But McCain couldn't be buttered up. He voted "no" on repealing the Affordable Care Act and begged his colleagues in Congress to just work together already.
So great that John McCain is coming back to vote. Brave - American hero! Thank you John.— Donald J. Trump (@realDonaldTrump) July 25, 2017
"We're getting nothing done, my friends," he pleaded before taking a quick jab at Trump, "We are not the president's subordinates."
Round Eight: Trump answered the bell fuming. When he visited Phoenix this August, Trump tried his hand at passive-aggressive disses instead of just firing from the hip. Subtlety wasn't exactly his strong suit, though.
Trump continued to repeat that he wouldn't name any names because he was being "presidential" but he lamented on being just "one vote away" from scrapping health care for millions of Americans.
From that point on McCain was quick to point out Trump's flaws, including the way the president used Twitter to announce that more than 2,000 service members could no longer serve because of their transgender identity.
Round Nine: Monday night, McCain cut to the core of Trump's America First mentality and called it "half-baked, spurious nationalism" in what CNN dubbed a "total and complete takedown of Trumpism" during his acceptance speech Monday night in Philadelphia.
Trump counter-punched, of course.
And the beating goes on.