WASHINGTON — President Trump has often seen the political benefits of stigmatizing Muslims.

During the 2016 campaign, he would not rule out creating a registry of Muslims in the United States. He claimed to have seen “thousands” of Muslims cheering on rooftops in New Jersey after Sept. 11, a statement that was widely debunked. And after the deadly attacks in Paris and California, Mr. Trump called for a moratorium on Muslims traveling to the United States.

“I think Islam hates us,” Mr. Trump told Anderson Cooper, the CNN host.

Now, with 19 months until the 2020 election, Mr. Trump is seeking to rally his base by sounding that theme again. And this time, he has a specific target: Representative Ilhan Omar, Democrat of Minnesota and one of the first Muslim women elected to Congress.

In Ms. Omar, a Somali refugee whose family received asylum in the United States when she was a teenager, Mr. Trump has found a perfect foil: a progressive whose embrace of the boycott-Israel movement and attacks on supporters of the Jewish state have already made her a divisive figure within her own party. As the first woman to wear a hijab on the House floor — she pushed for a rules change to allow it — she is also a powerful, and visible symbol for Muslims and refugees.

Mr. Trump and his team are trying to make Ms. Omar, who is relatively unknown in national politics, a household name, to be seen as the most prominent voice of the Democratic Party, regardless of her actual position. In February, the president pounced when Ms. Omar unleashed a firestorm with her comments on Israel, rejecting her subsequent apology and calling for her to resign.