A 50-50 party-line vote on Tuesday fell short of the 60-vote threshold needed to advance most legislation under Senate rules.

Democratic Senate Majority Leader Chuck Schumer set the bill as one of his party's top priorities, saying it could have offset a wave of measures passed by Republican-controlled state legislatures imposing new limits on voting.

Republican state legislators justify their new laws by citing former president Donald Trump's continued false claims that his November election defeat was the result of widespread fraud. Those claims were rejected by multiple courts, state election authorities and Trump's own administration.

"It is a fact, a fact that voting rights are under assault in America that we have not seen in many, many decades," Schumer said shortly before the vote started. "

Are we going to let reactionary state legislatures drag us back into the muck of voter suppression?"

Senator Joe Manchin of West Virginia had pushed for a bipartisan deal, even offering an alternative version of the bill that was not as far-reaching. But he failed to persuade a single Republican to open debate on the measure.

Anticipating failure in Tuesday's vote, some Democrats were already discussing alternative strategies for reining in the Republican efforts that reverse some of the 2020 election's expanded access for casting ballots.

Democratic House Majority Leader Steny Hoyer told reporters the likely Senate outcome "will be a dramatic evidence of why the filibuster needs to be modified."

He was referring to a procedure requiring at least 60 votes in the 100-member Senate to advance most legislation, instead of a simple majority of 51. The chamber is currently divided 50-50, with Democrats holding the tie-breaking vote in Vice President Kamala Harris.

Democratic Senator Debbie Stabenow alluded to possible legal action against Republican-led statutes in states, saying: "We have an attorney-general and a (Justice Department) Civil Rights Division and a commitment from the president of the United States. And we will continue on in every way we can."

But the courts may not provide an easy win.

The conservative-majority Supreme Court in recent years has made it more difficult to challenge both voting restrictions and the drawing of legislative districts.

In 2013, it gutted a key section of the Voting Rights Act that protects minority voters and in 2019 rejected efforts to rein in electoral map manipulation by politicians aimed at entrenching one party in power, a practice known as gerrymandering.

The court in coming days could further weaken the Voting Rights Act in a ruling on voting restrictions in Arizona.

Australian Associated Press