Sen. John McCain (R-AZ) doesn’t have much of a working relationship with President Donald Trump: “almost none,” he said on ABC’s The View Monday.

Instead, he’s more likely to swipe at the president — with frequent, biting lines.

“He is in the business of making money, and he has been successful both in television as well as Miss America and others,” McCain said of Trump in an interview with 60 Minutes last month. “I was raised in the concept and belief that duty, honor, country is the lodestar for behavior that we have to exhibit every single day."

McCain, the chair of the Senate Armed Services Committee and a veteran figure in Washington known for speaking his mind, hasn’t had many kind words about Trump from the start — a sentiment that has only escalated in recent weeks.

Over the weekend, McCain appeared to poke at Trump for deferring his Vietnam War draft order. Last Monday, accepting the Liberty Medal at an event honoring war heroes, McCain warned against "half-baked, spurious nationalism cooked up by people who would rather find scapegoats than solve problems" — a direct call against Trumpism. Just prior, he slammed the administration for missing the deadline to implement Russia sanctions. He spent the subsequent week in an open fight with the administration about the ambush in Niger that left four American soldiers dead, claiming Trump’s administration had failed to give the Armed Services Committee enough information about the attack.

"We did not know about Niger until it came out in the paper,” McCain told reporters. “We need to have a process of communications, which I've had with other administrations, of exchanging information and knowledge."

Trump has since responded to McCain’s recent comments with a warning.

“People have to be careful because at some point I fight back," the president said last Tuesday on The Chris Plante Show. "I'm being very nice. I'm being very, very nice. But at some point I fight back, and it won't be pretty."

Asked on The View if Trump’s threat scared him, McCain only laughed. The 81-year-old senator announced earlier this year that he has been diagnosed with a rare form of brain cancer that he is unlikely to recover from, returning from surgery only to vote down the Republicans’ health care effort in August. It makes the threat of a mean Trump look almost trivial.

McCain has long been one of the leading voices in a growing group of conservatives making a plea for respectfulness in politics — and against Trump. And there’s no sign of him stopping now.

McCain versus Trump has a long history

McCain’s tenuous political relationship with Trump has a long history. It famously began on the campaign trail, when Trump claimed McCain — a decorated naval aviator who was held prisoner during the Vietnam War for more than five years — was not a “war hero,” after the Republican senator commented that Trump’s campaign was founded on invigorating the “crazies.”

“He’s not a war hero,” Trump said at a presidential forum on the campaign trail. “He’s a war hero because he was captured. I like people who weren’t captured.”

At the time, Trump’s political prospects seemed near impossible. He had disparaged the career of a prisoner of war and former nominee of the political party he hoped to lead. His campaign was one gaffe after another. Then he became the Republican nominee.

McCain formally withdrew his support of Trump after the infamous Access Hollywood tape, in which the Republican nominee bragged about sexual assault, went public. New York magazine put McCain on their cover just after Trump’s inauguration, portraying him as Trump’s chief rival. Since then, McCain has remained a vocal critic of Trump.

When investigations into Trump’s alleged ties to Russia were first escalating earlier this year, and every week had a new bombshell report on the secret dealings of the president’s inner circle, McCain said the Trump administration’s scandals were “reaching Watergate size and scale.”

He was the deciding vote crushing the Republicans’ Obamacare repeal-and-replace bill and was vocal supporter of Congress’s Russia sanctions bill, which Trump begrudgingly signed — and accused the administration of delay tactics when they missed the deadline to implement the sanctions. McCain has spoken out against Trump’s travel ban and has apologized to foreign leaders for Trump’s diplomacy flubs. He called out the administration for falsely overselling the success of a raid in Yemen.

Trump has noticed. After McCain said the Yemen raid was a failure, Trump tweeted that the senator’s comment “emboldens the enemy.” In a rally in Arizona in late August, he took another verbal swing at McCain in front of his home crowd for tanking the health care bill.

Trump’s public censuring hasn’t stopped McCain from critiquing the president.

“We should not be fighting about a great American who lost his life fighting this country,” McCain said Monday about Trump’s current feud with a Gold Star widow, continuing what has been a longstanding gripe about Trump’s lack of civility.

He spent the past week slamming the Trump administration for failing to fully inform the Senate Armed Services Committee and the American public about the ambush in Niger that killed four American soldiers.

“Americans should know what is going on in Niger,” McCain said. He threatened to use subpoena power last Thursday if the administration did not come forward with more information, but said he had since had good conversations with high-ranking military officials. Still, he said, the Trump administration hasn’t been transparent.

"Actually, it was easier under Obama," McCain said of Trump’s administration. "I'm very close to these people. We converse all the time. [National Security Adviser] Gen. [H.R.] McMaster was in to see me yesterday. We're just not getting the information in a timely fashion that we need."

McCain and the rest of the Trump critics have something in common

McCain is among the growing ranks of conservatives making a call for respectful dialogue in Washington — a direct criticism of Trump.

In Congress, there’s Sen. Bob Corker (R-TN), who in recent weeks has questioned Trump’s fitness for office and compared the White House to an “adult day care.” In the House, Rep. Charlie Dent (R-PA) has said Republicans “say things privately they don’t say publicly” about Trump. Others, like Sen. Jeff Flake (R-AZ), have also taken swings; Flake wrote a scathing review of the Trump era of Republican politics in his recently published book Conscience of a Conservative.

Among the political veterans, George W. Bush gave a speech last week echoing many of McCain’s sentiments. “We’ve seen nationalism distorted into nativism, forgetting the dynamism that immigration has always brought to America,” the former president said in New York.

But these men all have something in common: Their political futures are nonexistent, or at best, highly in flux.

McCain is a sitting senator with a terminal illness, Corker recently announced he won’t be running for reelection, and Dent, too, is retiring. Flake, who is running, is sitting in one of the most vulnerable 2018 Republican Senate seats.

It’s a trend that’s persisted from the campaign days: The defining characteristic in the clear divide between Republicans willing to speak out against Trump and those who have supported him is political future.

For active Republican politicians, to go against Trump they must either defy their voter base or criticize aspects of the GOP ideology. Flake is already experiencing the danger of doing this, getting vigorously attacked by a pro-Trump right-wing candidate in his primary.

We saw attempts at this during the presidential election: Sen. Ted Cruz patently avoided a Trump endorsement at the Republican convention while trying to speak to the future of the Republican Party and saw his favorability rating plummet. (Cruz eventually caved and endorsed Trump.)

Trump’s affinity for sparking moral outrage, and his administration’s repeated policy flubs, has forced sitting politicians into a political calculus. According to one aide working on what looks like a contentious Republican 2018 seat: “How do we criticize him enough — because it’s the right to do — to politically insulate ourselves but continue to work with him for our legislative priorities?”