Senate Democrats failed again to pass sweeping new voting protections on Wednesday, in what may be the most brutal blow yet to efforts to strengthen protections for voters at a perilous moment for US democracy.

Just as they have done four other times in recent months, all 50 Republicans united in their opposition to the measure. They relied on the filibuster, a Senate rule that requires 60 votes to advance legislation to a final vote.

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Despite heavy pressure from Joe Biden and fellow Democrats, two senators, Joe Manchin and Kyrsten Sinema, have dug in defending the measure, preventing Democrats from getting rid of it.

In a rebuke to Biden, Sinema gave a speech on the Senate floor last week making it clear she would not support changes to the filibuster. Manchin has also consistently made his support clear. “I will not vote to eliminate or weaken the filibuster. The filibuster plays an important role in protecting our democracy from the transitory passions of the majority and respecting the input of the minority in the Senate,” he said in a speech on Wednesday.

Their opposition set up a showdown as the ultimately doomed bill was taken up for discussion on Wednesday. Late in the evening, Republicans used the filibuster to vote to end debate on the bill, effectively blocking it from advancing. Immediately afterwards, Democrats moved to hold a vote to try and change the filibuster rules anyway. The effort failed 52-48, with Manchin and Sinema voting with all 50 Republicans to preserve the filibuster. Sinema loudly said “aye” when it was her turn to vote in favor of preserving the filibuster changes.