"I think I might write in Lindsey Graham," McCain said Monday at a debate against his challenger in the Arizona senate race, Rep. Ann Kirkpatrick. "He's an old, good friend of mine and a lot of people like him. The fact is I can't, seriously, I cannot vote for either one."
McCain withdrew his support of Donald Trump over the weekend after a recording surfaced in which the Republican presidential nominee can be heard making vulgar comments about women.
On Tuesday, Trump hit back at the Arizona senator.
"The very foul mouthed Sen. John McCain begged for my support during his primary (I gave he won)," Trump tweeted
, "then dropped me over locker room remarks!"
McCain, a former GOP nominee in his own right, has said he also cannot support Trump's opponent, Hillary Clinton.
"It's not pleasant for me to renounce the nominee of my party, he won the nomination fair and square," McCain said at the debate. "But this, I have daughters, I have friends, I have so many wonderful people on my staff, they can not be degraded and demeaned in that fashion. And so I believe that ... I had to withdraw my support just as I cannot support Hillary Clinton."
So that might leave McCain with Graham, the South Carolina senator who ran a quixotic and short-lived campaign for the GOP presidential nomination.
When Graham ended his White House bid at the end of last year, McCain said that he and fellow Republicans lost "our most qualified, thoughtful, fearless and honest presidential candidate."
Such admiration was hardly surprising. The senators have had a famously close relationship for years, frequently teaming up on policy matters and making joint press appearances. With former Sen. Joseph Lieberman, the trio formed the so-called "three amigos."
As he seeks his sixth term in the Senate, McCain is strongly favored in his re-election bid against Kirkpatrick -- although many analysts have questioned whether Trump could influence the state of play in Arizona.
McCain, for his part, has never been a full-throated Trump supporter. At the debate on Monday night, the senator expressed concern for the future of his party.
"I just worry about, frankly, and this probably has nothing to do with this debate, but I worry about the future of the Republican party," McCain said. "We're gonna have a lot of work to do after this election is over."