Donald Trump arrives at Republican National Committee headquarters for a meeting with Speaker Paul D. Ryan (R-Wis.) and other House Republicans on July 7, 2016. (Mark Wilson/Getty Images)

Donald Trump came to Capitol Hill on Thursday to build and reinforce bridges with members of Congress less than two weeks before the Republican National Convention. Instead, he burned some to the ground.

During a closed-door meeting with Republican senators on Capitol Hill, Trump admonished three of them who were not backing him as the presumptive GOP nominee. He characterized Sen. Mark Kirk of Illinois as a loser and singled out Sen. Ben Sasse of Nebraska for opposing him, according to officials with direct knowledge of the exchanges.

The sharpest confrontation came with Sen. Jeff Flake of Arizona. “You’ve been very critical of me,” Trump said after Flake introduced himself.

“Yes, I’m the other senator from Arizona — the one who didn’t get captured — and I want to talk to you about statements like that,” Flake responded, referring to Trump’s dismissal of Sen. John McCain’s time as a prisoner of war in Vietnam.

Trump responded that he has yet to attack Flake hard but threatened to begin doing so. He also predicted Flake would lose reelection; Flake informed him he was not on the ballot this year.

Sen. Ben Sasse (R-Neb.) leaves a meeting with Trump at the Republican National Senatorial Committee headquarters. Sasse has declined to support Trump. (Zach Gibson/Getty Images)

Amid these and other combative exchanges, Trump made some progress with one holdout: Sen. Ted Cruz of Texas. After they held a separate meeting, Cruz spokeswoman Catherine Frazier said that while there was no talk of an endorsement, Trump asked Cruz to speak at the convention and he agreed to do so.

Republican leaders had hoped Trump would project polish and party unity. Instead, he has spent much of his time picking a series of personal fights with fellow Republicans and the media that have overshadowed his attempts to draw favorable contrasts with Democratic rival Hillary Clinton.

For Trump and his party, the timing could hardly be worse. The criminal investigation into Clinton’s use of a private email server was thrust back under the national spotlight this week when FBI Director James B. Comey scolded her for “extremely careless” practices.

“Just leaving D.C. Had great meetings with Republicans in the House and Senate,” Trump tweeted Thursday afternoon, giving no hint of the conflict that unfolded. “Very interesting day! These are people who love our country!”

Paul Manafort, the Trump campaign’s chairman and senior strategist, attended the meeting and disputed the portrayal of it as contentious. In a statement to The Washington Post, Manafort said, “Today’s meeting was positive and productive and these characterizations, attributed to unnamed sources, are wholly inaccurate.” He said attendees were in “total agreement” with Trump about the need to unify the party.

But Republican officials with direct knowledge of the Senate meeting told a much different story. The meeting grew combative as Trump upbraided Flake, Sasse and Kirk, according to the officials who were granted anonymity to describe the private gathering. He predicted each would lose his seat in November; only Kirk is up for reelection this year.

The tension was particularly high when Flake, who has voiced concerns about the businessman’s rhetoric and policies on immigration that the senator argues alienate many Latino voters, engaged with Trump.

Flake told Trump that he wants to be able to support him — “I’m not part of the Never Trump movement,” the senator said — but that he remains uncomfortable backing his candidacy, the officials said.

The Arizonan urged him to stop attacking Mexicans, prompting Trump’s retort about Flake losing reelection.

Flake confirmed the details of his exchange with Trump to reporters.

“My position remains, I want to support the nominee,” Flake said. “I really do. I just can’t support him given the things that he’s said.”

Trump also called out Kirk — who withdrew his endorsement of Trump last month, citing the business mogul’s racially based attacks on a federal judge — and said he did not approve of the senator’s action, the officials said.

Trump vowed that he would carry Illinois in the general election even though the state traditionally has been solidly Democratic in presidential contests. Kirk did not attend the meeting with Trump.

Asked later in the day about Trump’s comments, Kirk declined to comment other than to say, “I guess he lit me up.”

Sasse — who has refused to support Trump and has emerged as perhaps the most vocal advocate for a third-party candidate — did not engage with Trump’s criticisms in the meeting and was quiet on the way out.

“Senator Sasse went to today’s meeting ready to listen. Senator Sasse introduced himself to Mr. Trump, and the two had a gracious exchange,” said James Wegmann, the senator’s spokesman. “Mr. Sasse continues to believe that our country is in a bad place and, with these two candidates, this election remains a dumpster fire. Nothing has changed.”

Trump’s trip to Washington on Thursday highlighted the lingering concerns among congressional Republicans over controversial remarks he continues to deliver on the campaign trail and how they may affect GOP members facing tough reelection battles.

More than a dozen senators skipped the meeting. Of 54 Republican senators, 41 attended, according to Don Stewart, a spokesman for Senate Majority Leader Mitch McConnell (R-Ky.)

Before his meeting with senators, Trump visited with House Republicans in what leaders billed as a chance for rank-and-file members to get to know him better before the upcoming congressional recess.

Trump was greeted by applause from more than 200 House GOP members at the standing-room-only gathering, according to GOP aides, and was introduced at the event by TV personality Larry Kudlow.

Several lawmakers at the meeting said questions were raised about derogatory comments Trump has made about minorities and women, as well as his inability to stay on message.

Trump defended praising Iraqi dictator Saddam Hussein this week for being “so good” at killing terrorists. He said he thinks it was the only thing that was good about a “bad guy, really bad guy.”

Rep. Adam Kinzinger (R-Ill.) said Trump brought up the Hussein comments “in the context of how unfair the media has been to him.” Kinzinger called Trump’s comments about Hussein “disgusting and despicable.”

Speaker Paul D. Ryan (R-Wis.) cast the House meeting as a step in the right direction.

“What I thought was especially helpful today was our members just got access and got to ask their questions and talk about their issues,” Ryan said. “I thought he did a great job engaging with our members, and I think our members appreciated it.”

Several lawmakers leaving the meeting said they are still unconvinced that Trump can be a good standard-bearer for the party.

“I still need to be persuaded,” said Rep. Charlie Dent (R-Pa.), a centrist.

Rep. Mark Sanford (R-S.C.) left the meeting worried about Trump’s grasp on the basics of the Constitution.

“I wasn’t particularly impressed,” Sanford said at a lunch with reporters afterward. “It was the normal stream of consciousness that’s long on hyperbole and short on facts. At one point, somebody asked about Article I powers: ‘What will you do to protect them?’ I think his response was, ‘I want to protect Article I, Article II, Article XII,’ going down the list. There is no Article XII.”

Others expressed confidence that Trump understands he needs to tone down his rhetoric.

“If you look at the trajectory of his unforced errors, he’s getting better,” said Rep. Bill Flores (R-Tex.). “I mean, he’s not where we want him to be, but he’s getting better.”

The meetings followed a rally in Ohio on Wednesday night in which Trump said it was a mistake for his campaign to remove a tweet attacking Clinton with a six-pointed star placed on top of a bed of money. The image was circulated last month on an online Web forum frequented by white supremacists and has been widely condemned as anti-Semitic.

Trump said it was “just a star,” not the Jewish Star of David. He blamed media outlets that covered the controversy for “racially profiling.”

House members leaving Thursday’s meeting said Trump did not address the Star of David controversy in his remarks and was not asked about it by members.

When asked whether he was bothered by the tweet, Rep. Lee Zeldin (R-N.Y.), a Trump supporter and the only Jewish Republican in Congress, said, “I don’t think it helps him.”

When Senate Republicans reconvened inside the Capitol for their regular Thursday luncheon, most tried to portray the Trump meeting as productive.

Sen. John Thune (R-S.D.), the third-ranking leader, called it a “frank discussion” and “the kind you have inside the family.”

Sen. Bob Corker (R-Tenn.), who has emerged as a rare surrogate on behalf of Trump, said, “Generally speaking it was very productive.”

When asked why so many of Trump’s meetings end up with clashes, Corker paused for five seconds before saying, “Things end up always being memorable.”

Kelsey Snell, David Weigel and Karoun Demirjian contributed to this report.