Former defense secretary Jim Mattis’s unequivocal rebuke of President Trump is significant not just because of his standing in the U.S. military, but because he’s so revered among Republicans. Mattis was an unconventional choice for Trump’s first defense secretary, but one that was lauded by Republican lawmakers.

After Trump nominated him, Congress even passed legislation to allow Mattis to serve — current law requires the head of the Pentagon to be a civilian for at least seven years; Mattis, a retired Marine Corps general and head of U.S. Central Command, had been out of military service for only three. Led by Republicans, Congress gave Mattis an exception.

Then Mattis sailed through his confirmation hearing in the Republican-controlled Senate Armed Services Committee. It was then led by the late senator John McCain of Arizona, who was a big fan of Mattis. But other Republicans described Mattis in a way that made it seem like they thought he could do no wrong.

"I’ve been honored to have known you for 30 years,” said Sen. James M. Inhofe (R-Okla.) at the hearing. “I’m so excited that you’re willing to do this.”

Sen. James M. Inhofe (R-Okla.) in January 2017 praised Jim Mattis for his willingness to become defense secretary under President Trump. (C-SPAN)

“I think Secretary Cohen’s characterization of Braveheart couldn’t more perfectly put your personality and legacy in proper perspective,” said Sen. Thom Tillis (R-N.C.), referring to a comment made by William Cohen, a secretary of defense under President Bill Clinton.

“I was very impressed with our conversation this week, with your humility and your acuity to the global situation today,” said Sen. David Perdue (R-Ga.). ”... Thank you so much for your perspective, your willingness to serve, and for what you’re going to do for our country in the next decade.”

Mattis was confirmed by a vote of 98-to-1 on Trump’s Inauguration Day.

A year and a half later, Mattis was receiving an award from the International Republican Institute, and Sen. Lindsey O. Graham (R-S.C.) was asked to speak about Mattis. The moment called for Graham to heap praise on Mattis, and he did.

“You’re somewhere between Ronald Reagan and the Pope,” Graham said, referring to previous award winners. “You’re a Marine’s Marine. You’re a man’s man. You’ve got a heart of gold. … One thing I can tell you about the general: Don’t play him, you’ll regret it.”

But Graham gave Mattis more than just character praise. He said Mattis was one of the few leaders in Washington that other leaders in Washington listened to. “There are very few people you can quote that the Senate and House cares about. When General Mattis speaks as secretary of defense, people listen,” Graham said.

And Graham said Mattis’s gravitas was earned because of the values he holds, saying: “Mattis taught me that safety really comes when people have the ability to speak out, when they have a voice. … You understand freedom. You have fought for it. And you are wise enough to tell those of us in Congress that our values keep us free.”

At the end of 2018, when Mattis abruptly resigned over a conflict with Trump about whether to pull U.S. troops out of Syria, the top House Republican had kind words for him. “So much of what has happened and the success of America in the last few years, he’s been a part of,” Rep. Kevin McCarthy (R-Calif.), now the House minority leader, told Fox News. “ … This man has served his country well and he has fans on all sides of the aisle.”

So did Trump, who tried to part with Mattis on good terms and tweeted: “General Mattis was a great help to me in getting allies and other countries to pay their share of military obligations.”

On Thursday, Trump tried to rewrite that history in two tweets, trying to take credit for what his Republican allies saw in Mattis — right down to his nickname.

Now that Mattis has firmly put himself in the anti-Trump camp, calling his leadership immature and his presidency divisive, Republican lawmakers aren’t going as far as Trump. But they’re certainly not giving him as much credit as they used to.

Graham, who two years ago indicated Mattis had impeccable judgment about American ideals, suggested on Thursday on Fox News that Mattis was misguided: “General Mattis, I think you’re missing something here, my friend. You’re missing the fact that the liberal media has taken every event in the last three and a half years and laid it at the president’s feet. I’m not saying he’s blameless, but I am saying that you’re buying into a narrative that I think is quite frankly unfair.”

Inhofe is now the chairman of the committee that confirmed Mattis. When reporters asked him Thursday what he thought, Inhofe said Mattis was “encumbered” in the job and downplayed his comments as if Mattis were a disgruntled former employee: “Once you’re fired, sometimes that affects your attitude.”

Sen. John Neely Kennedy (R-La.) also questioned Mattis’s judgment, specifically on speaking out now.

But Mattis’s rebuke has made some ripples in the Senate. He opened the door to some senators who had already criticized Trump in the past for specific issues and comments to join Mattis in criticizing Trump’s entire presidency. That’s a new dynamic, and even though it’s only coming from a few Republican senators, it’s not a good one for Trump.

Sen. Lisa Murkowski (R-Alaska) told The Washington Post’s Paul Kane: “I was really thankful. I thought General Mattis’s words were true and honest and necessary and overdue.” She said she was “struggling” on whether she could continue to support Trump.

Certainly Murkowski and other senators have felt that way privately for some time. But to say it publicly is a step that Trump’s critics have long understood they can’t safely take if they want to stay in office. Murkowski isn’t up for reelection this year, which may afford her some room to say this now. But Trump voters have shown they have a long memory (putting some Republican lawmakers who ditched Trump after the 2016 “Access Hollywood” tape on notice in primaries). And even if Trump loses in November, there’s no guarantee that Trumpism will leave the party.

Murkowski wasn’t the only Republican senator to embrace what Mattis said. Sen. Mitt Romney (R-Utah), who voted to convict Trump on one charge in his impeachment trial, offered Mattis the kind of praise that his colleagues gave the defense secretary in 2017, telling reporters: “I think he’s an American patriot of extraordinary service and sacrifice and great judgment.”

Just three years ago, almost every Senate Republican would have agreed.