But they've broken with Trump on a number of issues in the past, including Russia.
They've criticized his baiting of white supremacists after deadly protests in Charlottesville, griped about the trade wars he's trying to start with tariffs, condemned his arguably racist comments about Mexico and other countries and been disgusted by him over the Access Hollywood tapes.
With the exception of Russia -- lawmakers forced sanctions on Trump a year ago -- there's not much Congress has done to rein him in. And many of those Republicans that have advocated more direct opposition to Trump will be out of a job next year.
The outrage at his performance in Helsinki was immediate and nearly unanimous, even among Republicans.
"There is no moral equivalence between the United States and Russia, which remains hostile to our most basic values and ideals," said Speaker of the House Paul Ryan, who is retiring soon.
Ryan's comment was a direct contradiction of Trump over the issue of Russia attacking the US election that sent Trump to the White House in 2016. Asked if he holds Russia accountable for anything at all during that appearance with Putin, Trump said the US and Russia both bear some blame.
Nebraska Republican Sen. Ben Sasse, long a Trump critic, called the comment "bizarre and flat-out wrong."
Arizona Republican Sen. John McCain called the whole Trump appearance "disgraceful," and so did Utah GOP Senate candidate Mitt Romney, who added that Trump's actions were "detrimental to Democratic principles."
Mitch McConnell, the top Senate Republican, was, as is his style, gentler and careful in his wording when he said that the Russians are "not our friends."
Rep. Trey Gowdy, the Republican in charge of oversight in the House, said he hoped those around Trump would help him see the light.
"I am confident former CIA Director and current Secretary of State Mike Pompeo, DNI Dan Coats, Ambassador Nikki Haley, FBI Director Chris Wray, Attorney General Jeff Sessions and others will be able to communicate to the President it is possible to conclude Russia interfered with our election in 2016 without delegitimizing his electoral success," Gowdy said in a statement.
There you have it. So what's next? Probably not much. As for any long-term rift between Republicans and the White House, lawmakers have already broken with Trump repeatedly during his candidacy and his time in White House and they have always come back home to him.
And there's every indication this lashing out will be as temporary as the others.
Take Gowdy. Days before lining up behind the intelligence community and Justice Department, he was chief inquisitor of Peter Strzok, the disgraced FBI agent who used to work on the Russia investigation and who Republicans argue showed anti-Trump bias.
Granted, Strzok does not look good in exchanging text messages with a colleague and lover. But put those text messages in the hands of a prosecutor like Gowdy, and the conspiracy theories about a "deep state" out to get the President really start to sing.
You cannot completely separate the work Gowdy did on Trump's behalf delegitimizing the Russia investigation last week with his written statement this week expressing frustration about Trump's warmth to Russia.
Those two things are linked.
Or take Romney, whose very public history with Trump has gone from highs, like Trump's very public endorsement of Romney for president in 2012 (he lost, as Trump likes to point out), to Romney's attempt to Brutus his party's likely nominee in 2016. When efforts to sabotage Trump's campaign failed, Romney considered taking up the secretary of state position, but was passed over by Trump.
Now he's running for Senate, but he's not opposing Trump on everything. Far from it.
Romney actually laid out exactly what's happening now in an op-ed in the Salt Lake Tribune earlier this year. He said, basically, he'll oppose Trump when he needs to, criticize him when he wants to, but he won't be forgetting they're on the same team.
"On one hand there are those who believe supporting the Trump agenda means supporting every policy the President proposes, whether or not they actually agree with that policy. It means refraining from criticizing anything the President says or does. The argument for this position is that you pick a team, so to speak, and when the leader of the team is criticized, his or her power to act is weakened and the opposition helped. So in order to achieve Republican policy aims, solid Republicans should stand with the President 100 percent, or at least stay silent when in disagreement.
"I take a different course. I will support the President's policies when I believe they are in the best interest of Utah and the nation."
By Romney's outline, Russia is one of those policy areas where he disagrees with the President. There will be others where he agrees. Tax cuts, perhaps, or Obamacare or the Supreme Court. He's perfectly happy separating these out.
Notably, the loudest voices opposing Trump in the GOP are headed for the exits. Bob Corker, the Senate Foreign Relations Committee chairman who has long criticized Trump, wants to clip the President's wings on trade. He unveiled a bill to rein in Trump's power to unilaterally impose tariffs (which Trump has gleefully deployed to tempt trade wars China, the EU, Mexico and Canada).
After Trump's brutalization of NATO last week and his cozying up to Putin this week, Corker called again for a vote on the measure. But McConnell and Ryan, neither of whom are great fans of Trump's tariffs, sound very much like they won't be voting on Corker's more binding proposal any time soon, although after Trump's Russia performance, his usual supporter Sen. Orrin Hatch sounded more open to a law curbing Trump's tariff authority.
Neither Corker nor Hatch will be around next year to push it. He's leaving the Senate rather than face a pro-Trump primary. So is Arizona Republican Jeff Flake, another Trump critic.
Senators did pass this month a non-binding resolution in the Senate asking the President to consult them before using national security as an excuse to invoke new tariffs.
It's another example of Republicans being happy to complain, even publicly, about Trump, but unlikely to do much more than that.
Russia has been the exception to the rule of the bark emanating from the GOP not resulting in any bite.
It was about one year ago that lawmakers sent legislation slapping new sanctions on Russia to Trump's desk, which blocked Trump from easing certain sanctions on Russia. He called it "seriously flawed" for encroaching on his ability to negotiate.
The law also sought to force new sanctions on Russia. But the White House has slow-walked the implementation of them. The Treasury Department announced new actions under the law in March.
But the administration's implementation included a list of oligarchs literally identical to a list printed earlier in Forbes. That doesn't exactly sound like something they're taking completely seriously.
Republican leaders will have to temper any efforts to rebuke the White House and impose new sanctions on Russia -- which is possible, but would not happen immediately -- with their efforts, like in Romney's case, to work with him on a host of other issues, like immigration, averting a government shutdown and getting Supreme Court nominees seated.
It's also hard to see much big legislation getting through Congress this close to an election year when the Senate is already going to be busy with the nomination of Brett Kavanaugh to the Supreme Court and overdue spending bills.
The trend among Republicans running for office has been to embrace Trump, by the way, not oppose him.
Is it possible the public and the Republican base are horrified by Trump's appeasement of Putin? Yes. But that would buck the trend of Republicans coming to terms with Trump as their leader. He delivered them the White House and they hold both houses of Congress, at least until November. If they want to keep either one, they'll need the voters who support Trump to show up and vote.
All of which suggests it will be very interesting to watch Republicans wrestle with turning their public rebukes their President on Russia into any definite action.