US Republicans have torpedoed a Democratic bid to implement nationwide election rules, a cherished priority of President Joe Biden's party.
The huge bill - which sought to make it easier for Americans to vote - ended up deadlocked 50-50 along party lines.
Biden said the issue was the "fight of his presidency", but some Democrats accuse him of not fighting hard enough.
Advocates say the bill would have been the most far-reaching election measure since the Voting Rights Act of 1965.
It comes as Republican-led states advance proposals - which Biden has depicted as racially discriminatory - to tighten election laws, and as former President Donald Trump, a Republican, continues to peddle unfounded claims that the 2020 election was stolen from him.
The Democrats' For the People Act passed the House of Representatives in March in a near party-line vote, with one Democrat joining all Republicans in opposing the bill.
But 60 votes are needed in the 100-member Senate to advance most legislation, and the upper chamber is evenly split 50-50 between the two parties.
Vice-President Kamala Harris, who has been assigned by the White House to push election reform, was presiding over the chamber as the bill failed.
"The fight's not over," she said after the vote.
The legislation would have introduced 15 days of early voting, made election day a public holiday, and guaranteed automatic voter registration for anyone with a driver's licence.
Democrats said the legislation would have also ensured more transparency for certain campaign contributions and limited partisan influence over the drawing of congressional districts.
The president's party argued the nearly 900-page proposal was critical to democracy, and would safeguard voting access for black voters.BBC
