Representative Steve Scalise of Louisiana withdrew on Thursday from consideration for the speakership he was on the cusp of claiming after hard-line Republicans balked at rallying around their party’s chosen candidate, leaving the House leaderless and the G.O.P. in chaos.
After being narrowly nominated for speaker during a Tuesday closed-door secret-ballot contest among House Republicans, Mr. Scalise, their No. 2 leader, found himself far from the 217 votes needed to be elected on the House floor. Many supporters of his challenger, Representative Jim Jordan of Ohio, the right-wing Republican endorsed by former President Donald J. Trump, refused to switch their allegiance.
With no clear end in sight to the G.O.P. infighting that has left one chamber of Congress paralyzed at a time of challenges at home and abroad, Mr. Scalise said he would step aside in hopes that someone else could unite the fractious party.
His abrupt exit left Republicans back at Square One, as fractured as ever over who should lead them and trading recriminations about the disarray in which they found themselves.
It came after an extraordinary few days on Capitol Hill that put Republican divisions on vivid display. Mr. Scalise had bested Mr. Jordan during the internal party contest by just 14 votes, and rather than consolidate his narrow base of backers, Mr. Scalise almost immediately began hemorrhaging supporters as lawmakers from several different factions let it be known they did not intend to fall into line behind him.
It did not help that Mr. Trump weighed in on Thursday against Mr. Scalise, arguing that the Louisianan was unfit for the speakership because he is battling blood cancer.
“Steve is a man that is in serious trouble, from the standpoint of his cancer,” Mr. Trump said on Fox News Radio, adding later, “I just don’t know how you can do the job when you have such a serious problem.”
Other top House Republicans had also refrained from publicly rallying around Mr. Scalise, instead allowing the resistance to him in their ranks to fester. Mr. Jordan never made a full-throated endorsement of Mr. Scalise, despite indicating his support. And Representative Kevin McCarthy of California, the ousted former speaker who has an icy relationship with Mr. Scalise, said the Louisiana Republican had overestimated his backing and might be unable to recover.
“It’s possible; it’s a big hill, though,” Mr. McCarthy told reporters at the Capitol as he entered a meeting with Mr. Scalise. “He had told a lot of people he was going to be at 150. He wasn’t there.”
It was the latest remarkable turn in a saga that has been marked by whiplash, shifting alliances and petty grudges. The situation has highlighted major changes in the nature of the House Republican conference, whose members once dutifully lined up in support of their chosen leaders but increasingly appear to be pursuing a strategy of every member for themselves.
The uncertainty has hobbled the House amid multiple crises, with U.S. allies at war in Israel and Ukraine and a government shutdown looming next month if Congress cannot reach a spending agreement.
Mr. Scalise has served in House leadership since 2014, and overcome great personal hardship to become the choice of a majority of Republicans to lead the chamber.
He was diagnosed with blood cancer over the summer and is now undergoing intense treatment, which has prompted him to wear a mask to vote on the House floor and attend news conferences. And in 2017, during a practice for a congressional baseball game, an anti-Trump extremist shot and seriously wounded Mr. Scalise. He still walks with a limp from the incident.
It was not clear whether he would leave his post as majority leader after his failed attempt to win the top post in the House, or try to remain in the No. 2 slot.