George Santos, the disgraced former congressman who was expelled from the House last year, said he was calling it quits with the Republican Party.

Mr. Santos made the announcement on Friday, after House Republicans made a deal with Democrats to avert a government shutdown, enraging far-right party members.

“The Republican Party continues to lie and swindle its voter base,” Mr. Santos, who has been charged with stealing from campaign donors, said in a post on X. “I, in good conscience, cannot affiliate myself with a party that stands for nothing and falls for everything.”

His declaration could, in theory, have an effect on the House race in the First Congressional District on eastern Long Island, where Mr. Santos had intended to mount a primary challenge against Representative Nick LaLota, a Republican and one of Mr. Santos’s fiercest critics in the House.

There has been little evidence that Mr. Santos had done much campaign work or fund-raising for the contest. Nevertheless, he said he would stay in the race and take his “Ultra MAGA/Trump supporting values to the ballot in November as an independent.”

If he does so, he could potentially draw some votes away from Mr. LaLota, which would benefit the undetermined Democratic candidate in a district that Donald J. Trump won by just under 2 points in 2020.

Even so, neither Mr. LaLota nor Jesse Garcia, the Suffolk County Republican Party chairman, seemed particularly concerned by Mr. Santos’s threat.

“George Santos is irrelevant to the electoral process,” Mr. Garcia said upon hearing the news, adding that the announcement was nothing more than a ploy for attention.

Mr. LaLota said in a statement that just as Mr. Santos’s expulsion had been good for the nation, his resignation from the Republican Party was good for “common-sense conservatives.”

He added: “Santos can watch the November election results from his prison cell.”

Mr. Santos was expelled from office in December by a rare two-thirds majority of his colleagues, after a House Ethics Committee report found that he had brazenly stolen from his campaign and used the money to buy Botox and luxury goods.

In the immediate aftermath of that expulsion, Mr. Santos declared himself done with Washington, but his resolve proved weak: He returned to the Capitol to attend President Biden’s State of the Union address, and declared his candidacy via social media that evening from the House chamber.

Mr. Santos faces 23 federal felony counts, including wire fraud, money laundering and aggravated identity theft, and could face up to 20 years in prison if convicted. His trial is set for September.