WASHINGTON — Joe Walsh, the conservative radio show host and former Tea Party congressman from Illinois who was running a presidential campaign challenging President Trump’s fitness for office, announced on Friday that he was ending his bid for the Republican nomination.
That leaves Mr. Trump with only one Republican challenger, former Gov. William F. Weld of Massachusetts.
“I am ending my candidacy for president of the United States,” Mr. Walsh said in an interview on CNN Friday morning. “I got into this because I thought it was really important that there was a Republican — a Republican — out there every day calling out this president for how unfit he is.”
Those calls, however, seemed to fall on deaf ears.
Mr. Walsh, who supported Mr. Trump in 2016 and ran as a former disciple who had seen the light, became a regular presence on cable news channels, calling Mr. Trump an “unfit con man” and a danger to the country. His hope was that he would create a permission structure for other former supporters to follow suit and change their minds about Mr. Trump.
But after spending the majority of his time campaigning in Iowa, Mr. Walsh got just 1.1 percent of the vote in the caucuses there on Monday, failing to make any dent in Mr. Trump’s support among Republican voters. (He finished behind Mr. Weld, who got 1.3 percent.)
The experience, he said, left him cynical about the future of the party.
“I spoke in front of 3,000 Iowa Republicans last night,” Mr. Walsh wrote on Twitter last week. “It was like a MAGA rally. I told them we needed a President who doesn’t lie all the time. The crowd booed me. I told them we needed a President who wasn’t indecent & cruel. The crowd booed me.” He said the experience made him realize “again that my Republican Party isn’t a Party, it’s a cult.”
Mr. Walsh, who entered the race last August, was once part of a trio of Republican challengers to Mr. Trump, who together were involved in a quixotic attempt to peel away support from a president with an iron grip on his party.
But Mr. Trump’s campaign operatives had worked for over a year to lock up support at the state level and make it impossible for any primary challenger to find sunlight. The state Republican parties in Arizona, Kansas, Nevada and South Carolina canceled their 2020 presidential primaries.
Even in Iowa, the state party chairman, Jeff Kaufmann, framed his caucus more as a test run for what he expects to be a competitive 2024 Republican field.
The tactics worked.
Last November, former Gov. Mark Sanford of South Carolina dropped out of the Republican primary, just two months after announcing his run.
Speaking from the White House on Thursday as he celebrated his acquittal in the Senate impeachment trial, Mr. Trump dismissed his remaining challengers as “non-people,” a rare acknowledgment that he had any competitors at all.
“We have two people running, you know, and I guess they consider them non-people, but they are running,” Mr. Trump told lawmakers who celebrated him in the East Room. “I mean, one was a governor. One was a congressman. They’re running. We got 98 percent of the vote.”
Mr. Weld’s campaign aides said they planned to soldier on alone.
“It’s hard to challenge a tyrant,” said R.J. Lyman, chairman of Mr. Weld’s campaign. “Joe Walsh is a very different person than Bill Weld, but is a good person and he made a good effort to explain how a Tea Party Republican could stand up to Trump. People weren’t willing to follow.”
Mr. Lyman said that Mr. Weld would stay in the race regardless of how he fares in the New Hampshire primary on Tuesday. “There’s no doubt that the independence and individuality of New Hampshire are traits we hope will pierce through the cultish obsession of the Trumpists,” he said.