Representative María Elvira Salazar, a Florida Republican, released a television ad on Thursday directly assaulting President Trump’s immigration crackdown, a rare and remarkable break and a warning sign for her party of eroding support among Hispanic voters.

“Mr. President, some of your immigration enforcement efforts have gone too far,” Ms. Salazar said straight into the camera. She later added: “The same Hispanics who helped you get to the White House in 2024 feel betrayed today.”

The decision by Ms. Salazar, a three-term representative from Miami, to record such an ad is striking given that she won re-election by 20 percentage points in 2024 and serves in the House Republican leadership as an assistant whip. Mr. Trump carried the district two years ago with 57 percent of the vote, and Ms. Salazar’s race in Florida’s 27th Congressional District has not been considered among the nation’s most competitive. But her ad — and its message — appear to be a sign of backlash to Mr. Trump’s immigration policy in Hispanic communities.

Even in South Florida, which has swung to the political right in recent election cycles, some Republicans have been raising concerns for many months that unpopular policies could cost some of them in the November midterms. Outside of Florida, Democrats are hoping to compete in four Texas districts with large Latino populations that Republicans redrew to be more favorable to their party. Mr. Trump endorsed Ms. Salazar for re-election earlier this year, writing on Truth Social, “SHE WILL NEVER LET YOU DOWN.”

Republicans have generally been reluctant to break with Mr. Trump, fearing both backlash from the president himself and from his supporters. Ms. Salazar faces a challenge from Eliott Rodríguez, a Democrat, in a matchup of parallel biographies: Both are Cuban American former broadcast journalists. Fernand R. Amandi, Mr. Rodríguez’s campaign strategist, accused Ms. Salazar of “lying” in the 30-second ad, which is also airing in Spanish. “She did this,” Mr. Amandi said in a statement. “She owns all of these deportations, ICE harassment and racial profiling. She voted for all this. She gave Trump the billions in ICE funding and the tools to do this. Don’t let her phony, eleventh-hour, ‘Alligator Alcatraz’ tears fool you because her boss’s immigration policy is now political poison in her re-election campaign.”

For months, she has been pushing other House Republicans to back a bipartisan bill that would give some immigrants with no criminal background a path to obtain legal status and work permits but not citizenship. That legislation has put her squarely at odds with immigration hard-liners more closely aligned with the party’s MAGA wing, who have blasted her for a bill that they call mass amnesty. Their criticism burst into public view during a congressional recess earlier this year, when Representative Brandon Gill of Texas began criticizing Ms. Salazar’s bill on social media, inciting a series of back-and-forth posts that eventually roped in other far-right Republicans. Ms. Salazar’s bill has support from more than a dozen Republicans, many of them in battleground districts where Mr. Trump’s immigration crackdown has been unpopular. South Florida has been rocked by federal and state law enforcement efforts to crack down on immigration, including the creation last year of a state-run detention facility in the Everglades known as Alligator Alcatraz. The facility closed this summer after proving costly and ineffective; a report released this week by the Department of Homeland Security’s Office of Inspector General found that the center failed to comply with a host of federal detention standards.