Former defense secretary Jim Mattis’s strong rebuke of President Trump forced Republicans to choose sides between a revered retired Marine Corps general and a leader with a near-stranglehold on the party and the voters critical to their election.

Mattis moved one senior Senate Republican to finally declare she had to speak out against Trump’s handling of the racial injustice protests, and against his moral leadership more broadly, while signaling she may not support him in November.

“When I saw General Mattis’s comments yesterday, I felt like perhaps we’re getting to the point where we can be more honest with the concerns that we might hold internally and have the courage of our own convictions to speak up,” Sen. Lisa Murkowski (R-Alaska), chair of the Energy and Natural Resources Committee, said Thursday.

Sen. Lisa Murkowski (R-Alaska) on June 4 praised former defense secretary Jim Mattis for criticizing Trump’s recent actions. (The Washington Post)

Murkowski, the 10th-longest-serving active GOP senator, told reporters that she agreed with Mattis’s broadside that Trump tries to deliberately divide Americans and the nation was “witnessing the consequences of three years without mature leadership.”

“I thought General Mattis’s words were true and honest and necessary and overdue,” Murkowski told reporters at the Capitol.

Her comments stood out among Republicans, who for the most part either remained silent in the wake of Mattis’s criticism, accused the media of trying to stir controversy or offered supportive words for Trump.

Yet it served as a stunning denunciation from within a party whose leaders on Capitol Hill have either marched in lockstep with Trump or ducked any of his controversial moves, to the point that Sen. Mitt Romney (Utah) was the only Republican to vote to convict Trump at his impeachment trial earlier this year.

Sen. Lisa Murkowski (R-Alaska) said on June 4 that she had been challenged for not speaking out about racial inequality sooner. (The Washington Post)

Romney initially avoided addressing the matter, but after Murkowski spoke out, he joined in criticizing Trump’s recent behavior by calling Mattis’s statement “stunning and powerful.”

“I think the world of him. If I ever had to choose somebody to be in a foxhole with — it would be with a General Mattis,” the 2012 Republican presidential nominee told reporters.

Late Thursday, Trump lashed out at Murkowski on Twitter, promising to campaign against her in Alaska in 2022 when she faces reelection. “Get any candidate ready, good or bad, I don’t care, I’m endorsing. If you have a pulse, I’m with you!” he wrote.

Most other Republicans decided to remain in Trump’s political foxhole, offering praise for Mattis’s more than four decades of military service but sidestepping his feud with Trump that occurred during two tumultuous years as secretary of defense.

These same Republicans had heralded Trump’s nomination of Mattis, seeing him as a stabilizing force in the mercurial president’s Cabinet. Congress went so far as to change the law so the retired general could serve in the civilian post despite being out of uniform for just over four years. The previous law had required seven years out of uniform for incoming defense secretaries.

The Senate approved his nomination 98 to 1 on the day Trump was inaugurated.

Sen. Lindsey O. Graham (R-S.C.) accused Mattis of “buying into a narrative” from the news media that everything wrong with the country is Trump’s fault.

“To 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,” Graham told Fox News.

In 2018, when he presented an award to Mattis, Graham said the Pentagon chief was “somewhere between Ronald Reagan and the Pope.”

“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.

Sen. James M. Inhofe (R-Okla.) told reporters that Mattis has “always been one of my favorite people” but said that his military background left him incapable of handling the internal political battles inside a West Wing overseen by an erratic president.

“He’d never been around that kind of environment, and consequently he was kind of encumbered from the very beginning of not really understanding the political enemy,” the chairman of the Senate Armed Services Committee said.

Inhofe had told Mattis at his confirmation hearing: “I’m so excited that you’re willing to do this.”

Sen. John Barrasso (R-Wyo.), a member of GOP leadership, said he had “a great deal of respect” for Mattis and John Allen, a retired four-star Marine general, but declined to address the contents of their sharp critiques of Trump.

“Everything I‘m focused on right now is things that are going to bring everybody together rather than divisiveness, and that’s what I’m focused on,” Barrasso told reporters.

Published merely hours apart, Mattis wrote in a story published in the Atlantic Wednesday that Trump “is the first president in my lifetime who does not try to unite the American people.” Allen published a Foreign Policy op-ed lambasting the president for his threats to use the military on protesters and his controversial church photo op on Monday, writing that his actions “may well signal the beginning of the end of the American experiment.”

Trump responded on Twitter on Wednesday night, criticizing Mattis in a pair of tweets that had at least two factual errors.

“Probably the only thing Barack Obama and I have in common is that we both had the honor of firing Jim Mattis, the world’s most overrated General. I asked for his letter of resignation, & felt great about. His nickname was ‘Chaos’, which I didn’t like, & changed it to ‘Mad Dog,’ ” Trump tweeted. “His primary strength was not military, but rather personal public relations. I gave him a new life, things to do, and battles to win, but he seldom ‘brought home the bacon’. I didn’t like his ‘leadership’ style or much else about him, and many others agree. Glad he is gone!”

Responding further to Mattis, Trump on Thursday tweeted a letter from his former attorney John M. Dowd, who was a captain in the Marine Corps and a member of the Judge Advocate General Corps. Dowd wrote to Mattis that his critique left him “appalled and upset.” and said the protesters outside the White House were “not peaceful and are not real,” calling them “terrorists.” Dowd criticized Obama and maintains that Trump has done more for minorities.

Another retired Marine general, John Kelly, who served as Trump’s chief of staff, stood by Mattis and rejected that assertion that Trump fired him, explaining Mattis resigned at the end of 2018 in a policy dispute over U.S. military presence in Syria.

“The president did not fire him. He did not ask for his resignation,” Kelly, a retired Marine Corps general, said in an interview with The Washington Post, calling Mattis an “honorable man.”

Senate Majority Leader Mitch McConnell (R-Ky.), who was a Mattis ally and declared he was “particularly distressed” by his 2018 resignation, ignored questions from reporters about the former secretary’s comments at Thursday’s Senate session. Senate Republicans did not discuss Mattis’s criticism of Trump at their closed-door policy lunch.

Other Republicans tried to explain the issue as a personality dispute that grew out of Mattis’s tenure running the Pentagon.

“I think it’s kind of obvious for some time that he and the president are at different wavelengths,” Sen. Pat Roberts (R-Kan.) said, suggesting that today’s political moment makes it hard for Trump to forge unity.

“I don’t share that view,” Roberts said of Mattis’s statement. “I think he’s doing the best he can under very difficult circumstances.”

But Mattis’s assault showed cracks in Trump’s armor that had not been seen since the GOP revolt after his remarks in 2017 when he praised white nationalists who caused riots in Charlottesville.

One of the party’s prized House recruits disagreed Thursday with Trump’s tone and how federal officers cleared the area outside St. John’s Episcopal Church Monday so that he could visit.

“I would like to see him lead by addressing the nation and call for everyone to come together,” Ashley Hinson, who won the GOP primary in Iowa’s 1st District on Tuesday, said. “I don’t have all the details of what happened, obviously, but I’ve seen the pictures and the video of what happened in Washington, D.C. I don’t believe people in a peaceful protest should be cleared for a photo op.”

Sen. Rob Portman (R-Ohio) said Trump’s “prepared remarks” have included calls for unity and also justice for the Floyd family, promising a fair prosecution of the police charges in the case.

“But his tone and words, kind of in between those more formal presentations, have not unified people, because it’s helped to push people,” Portman said.

And Sen. Charles E. Grassley (R-Iowa), frustrated with the administration’s failure to explain why Trump fired the intelligence community’s inspector general, blocked two of Trump’s nominees, a rare move by a GOP senator.

Murkowski’s break with Trump might be the strongest so far.

Romney has had a personal feud with Trump predating his presidency, as did the late John S. McCain (R-Ariz.) and former senators Jeff Flake (R-Ariz.) and Bob Corker.

By contrast, Murkowski is a moderate Republican who has occasionally bucked Trump on significant votes, such as confirming Supreme Court Justice Brett M. Kavanaugh, but has rarely taken her views public, hardly ever appearing on TV news shows.

On Thursday morning, barely prompted to respond to Mattis, Murkowski expressed relief that she was finally saying what she grappled with for several years.

“I am struggling with it. I have struggled with it for a long time,” she said whether she could vote for Trump in November.

“I think there are important conversations that we need to have as an American people amongst ourselves about where we are right now,” she added.

Josh Dawsey, Dan Lamothe and David Weigel contributed to this report.