Cheri Bustos, who leads House Democrats’ campaign arm, says she won’t seek another term as chairwoman.

Representative Cheri Bustos of Illinois, the leader of the House Democrats’ campaign arm, told colleagues on Monday that she would not seek another term as chairwoman after she led her party to unexpected losses last week and only narrowly won her own re-election race.

In a letter to colleagues, Ms. Bustos conceded she had “hoped for better results” and was “gutted at the losses we sustained” even as she noted that she had delivered on “job No. 1,” maintaining the majority.

Ms. Bustos will remain in her position in the coming weeks, as Democrats continue to battle for a dozen or so seats where vote-counting continues. But she said she would not seek any other leadership post days after Democrats from the party’s moderate and progressive wings traded blame over the losses on a caucus conference call.

“Instead, I will focus my efforts legislatively to help President-elect Biden and Vice President-elect Kamala Harris as we build back better for the people,” Ms. Bustos said.

Democrats had entered the election on the offensive, predicting they would grow their majority and protect all but a handful of incumbents in red-leaning districts. Instead, Democrats are on track to lose six to 10 seats and failed to capture almost every pickup opportunity.

The outcome was a painful and embarrassing turn for Ms. Bustos, 59, who was considered a rising star in the party who was particularly adept at devising strategies for Democrats running in conservative-leaning districts.

Her departure will clear the way for others competing for the campaign committee position. Already some Democrats are pitching Representative Tony Cárdenas of California for the post. Mr. Cárdenas, who represents the Los Angeles area, could potentially help the party reorient after losing significant ground to Republicans among Latino voters in Florida, Texas and some other states.

Representative Sean Patrick Maloney of New York, who is expected to win his district in the heart of Hudson Valley though it has not yet been called, formally announced his candidacy for the position, according to a letter obtained by The New York Times.

“My experience will allow me to better support our vulnerable members — especially our historically diverse group of frontline members — without sacrificing our shared principles,” Mr. Maloney wrote, citing his fund-raising, professional background and the makeup of his district as part of his pitch.

Ms. Bustos was still expected to convene a briefing for Democratic lawmakers on Tuesday to discuss the election results. In her letter, she said the campaign committee would conduct a review “to better understand why the national polling and modeling environment failed to materialize.”

In a statement, Speaker Nancy Pelosi praised Ms. Bustos as “a leader of great integrity and inspiration” and thanked her for her service.