WASHINGTON—The leader of Senate Democrats moved to take the threat of a government shutdown off the table, following a grueling intraparty fight in which lawmakers struggled with how best to resist President Trump’s fast-paced efforts to slim down federal agencies.

Veteran Democrats privately believed Chuck Schumer’s decision on the shutdown was inevitable. Others were ready for the top Senate Democrat to lead them into their first big battle against President Donald Trump — and instead have been left fuming.

Schumer relented one day after he vowed Senate Democrats would thwart the "partisan" measure, saying the "chaos" of a government shutdown would be a worse option.