He might not be done just yet.

Representative Thomas Massie, President Trump’s most prominent Republican critic in Congress, lost his primary last week in Kentucky to a challenger backed by the president. But Mr. Massie filed a statement of candidacy on Monday that will give him the ability to raise money for a potential run for office in 2028, according to Federal Election Commission records.

“This allows me to raise funds to continue my political operations supporting my position as a current office holder and as a potential candidate for federal office,” Mr. Massie wrote in a social media post.

While the form lists the office being sought as “House,” Mr. Massie wrote: “I haven’t made a final decision about which office to seek, if I run.”

Mr. Massie, 55, the libertarian-leaning, raw-milk-drinking, M.I.T.-educated engineer who was first elected to the House of Representatives in 2012, emerged as a thorn in Mr. Trump’s side during his second term. He was one of only two House Republicans to vote no on the president’s signature One Big Beautiful Bill, he led the push for the release of the Jeffrey Epstein files, and he has been a vocal opponent of the war in Iran.

In last week’s high-profile, high-dollar, revenge-fueled contest, he lost by 10 points to Ed Gallrein, a farmer and former Navy SEAL supported by Mr. Trump. (Mr. Trump claimed that he had told his staff to “just give me somebody with a warm body to beat Massie.”)

Buoyed by chants from undeterred supporters — “No more wars!” “America first!” “2028!” — Mr. Massie delivered a defiant concession speech after his defeat.

“There is a yearning in this country for someone who will vote for principles over party,” he said.

Senator Rand Paul, a Republican from Kentucky and an ally of Mr. Massie’s, is up for re-election in 2028. Mr. Paul, who ran for president in 2016, is considering another presidential bid. He said in March on “CBS News Sunday Morning” that he was “thinking about it” and that he was “50-50.”

On Sunday, on NBC’s “Meet the Press,” Mr. Massie was asked if he was considering a run for president in 2028. “I will not rule out anything, and right now I’m not going to rule in anything,” he told Kristen Welker, the host.

“I won’t rule out a run for county commissioner,” Mr. Massie added. “I used to be the county judge executive here. That was probably the best job I ever had in politics.”