Since her election in 2021, Wu hasn’t often sought out the national stage. But on Wednesday, as she was grilled over and over about one of the nation’s most contentious issues, Wu nonetheless showed she could hold her own when that spotlight shined on her, unafraid to either answer directly or try to provide more context if necessary.

Making her first congressional appearance, Wu appeared at ease, comfortable enough to nurse her newborn daughter in her witness seat before the hearing started and confident enough to fire back at Republicans several times when she believed they were misstating the facts.

Wu was at turns responsive and combative, defending the city’s policies while delivering the most direct answers and the sharpest retorts of the four mayors to attacks from Republicans who threatened to pull federal funding and investigate them for allegedly violating federal immigration law.

She even took a shot at President Trump’s “border czar,” Tom Homan, who recently denigrated Boston Police Commissioner Michael Cox and vowed to bring “hell” to Boston for not doing more to assist in federal deportation efforts.

“Shame on him for lying about my city,” Wu said, a cross of ashes on her forehead marking Ash Wednesday. “For having the nerve to insult our police commissioner, who has overseen the safest Boston’s been in anyone’s lifetime. Bring him here under oath, and let’s ask him some questions.”

Wu’s assertive performance drew praise from Democrats, including Massachusetts Representative Ayanna Pressley and New Mexico Representative Melanie A. Stansbury.

“She has a seven-week . . . old baby, and she showed up to testify and be yelled at by our colleagues for four hours,” Stansbury said during her questioning as the hearing dragged into the afternoon. “May your daughter grow up to be a fierce leader like you.”

Republicans weren’t as impressed. Mace called Wu a hypocrite for her policies. And Florida Representative Byron Donalds chastised Wu for not knowing how much the city spends on undocumented immigrants.

“Do you manage your budget or not?” Donalds responded after Wu said the city does not ask about immigration status when delivering services.

“The City of Boston is sick of having people outside Boston telling us what we need,” Wu shot back after noting the city has a triple-A bond rating.

After the hearing, which included two breaks that allowed Wu to nurse her baby in a back room, the mayor said she was happy to be flying home Wednesday night.

“I was proud to be able to share the story of Boston, the story of our residents, and to stick up for our city, especially in the cases where there was a lot of misinformation and a lot of assertions from people who haven’t been to Boston [and] don’t know our city,” Wu told reporters outside the hearing room.

Representative James Comer, a Kentucky Republican who chairs the House Oversight Committee, summoned the mayors because all four cities have laws that prevent their police from assisting in civil immigration enforcement for undocumented immigrants who are not wanted for violent crimes.

“President Trump and his administration are taking action against sanctuary cities,” Comer said to open the hearing. “And Congress must follow by not allowing a single penny of federal funding to go to cities and states that prioritize criminal aliens over the American people.”

The mayors rejected that framing. They stressed their police departments cooperate with federal immigration authorities when undocumented immigrants are wanted for criminal offenses. Wu noted the city’s Trust Act leaves enforcement of civil immigration violations to federal authorities. The other cities have similar laws.

Wu and the other mayors all said violent crime was down in their cities. Wu declared four times in her opening statement alone that Boston is the safest major city in the country and repeated that point several more times during the hearing.

“Every year since I took office, we’ve set a new record-low for gun violence in Boston,” she said. “Last year, Boston saw the fewest homicides on record in the last 70 years. Those are the facts.”

In her longer written statement to the committee, Wu cited data from the Major Cities Chiefs Association. A Globe analysis found that some violent crimes have declined dramatically in Boston since Wu took office in late 2021.

Wu struck a defiant tone from the start, defending the city’s immigration approach as successful and criticizing the Trump administration’s aggressive push to deport undocumented immigrants.

“This federal administration is making hard-working, tax-paying, God-fearing people afraid to live their lives,” Wu said. “A city that’s scared is not a city that’s safe. A land ruled by fear is not the land of the free.”

Wu also focused on the importance of immigrants to Boston’s history and its future.

“We are the cradle of democracy and the city of champions,” she said. “We are all these things not in spite of our immigrants, but because of them.”

Still, some Republicans accused Wu and her fellow mayors of violating federal immigration law. Florida Representative Anna Paulina Luna said she was referring all of them to the Justice Department for criminal investigation.

Peter Markowitz, codirector of the immigration justice clinic at Cardozo School of Law in New York, called Luna’s comments “a moment of political theater and an empty threat.”

“There is nothing about Boston’s sanctuary law, or any of the sanctuary laws at issue, that in any way exposes the city or its employees to federal prosecution,” Markowitz said. (The Wu administration does not use the term sanctuary to describe its immigration policy.)

Despite Luna’s threat, and the suggestion by Georgia Representative Marjorie Taylor Greene that all four mayors were guilty of treason, the hearing failed to deliver the nonstop fireworks promised by an explosive teaser video committee Republicans posted.

Comer told reporters afterward that it was up to each lawmaker to decide on criminal referrals. But he said his committee would continue to investigate immigration policies of the cities. “Federal funding is at risk if they continue to obstruct” immigration law, Comer said.

Although the threat remains, Wu’s team seemed to consider the hearing a success.

By midday, her social media accounts were blasting out video clips, including a sharp exchange with Arizona Republican Representative Paul Gosar, in which Wu called on Republicans in Congress to “stop cutting Medicaid, stop cutting cancer research, stop cutting funds for veterans.”

“If Republicans in Congress want to help make our country safe, I have some ideas for them,” the mayor’s account posted on Bluesky.

Her campaign also sent out a fund-raising email, posting a video of her opening statement on a donation page.

“Republicans are attacking her relentlessly over her commitment to making Boston a welcoming city to immigrants,” the campaign wrote. “Michelle Wu is expertly defending Boston.”

Wu is facing a reelection challenge from Josh Kraft, a longtime nonprofit leader and the son of billionaire New England Patriots owner Robert Kraft.

As she sat before the committee in Washington, Wu was bolstered by support from back home.

A group of religious leaders organized a morning prayer service for Wu, marking Ash Wednesday with scripture readings and songs at the Cathedral Church of St. Paul.

And on City Hall plaza, a crowd of more than 100 people gathered with signs that read “We are all immigrants,” “America runs on immigrants,” and “Give ‘em hell Michelle.” The gathering, which Kraft attended, drew about a dozen counterprotesters bearing Trump flags.

Niki Griswold of the Globe staff and Globe correspondent Emily Spatz contributed reporting.

Jim Puzzanghera can be reached at [email protected]. Follow him @JimPuzzanghera. Emma Platoff can be reached at [email protected]. Follow her @emmaplatoff.