Senate Republicans on Thursday blocked a vote on a constitutional amendment to overturn Citizens United and other Supreme Court rulings dating back to 1976 that invalidated restrictions on money in politics.

The party line vote was 54 in favor, 42 against, falling short of the 60 votes needed to defeat a filibuster and proceed to a final vote.

The Senate broke an initial filibuster on the measure on Monday. But many Republicans who voted to begin debate did not support the proposal and intended to ultimately block it. The procedural motion on Thursday means the Senate won’t move to an up-or-down vote, where it was even likelier to fail because it needed a two-thirds majority to advance.

Senate Minority Leader Mitch McConnell (R-KY), a fierce opponent of campaign finance restrictions, blasted Democrats for bringing up the measure.

“I have to say it’s a little disconcerting to see the Democrat-led Senate focusing on things like reducing free speech protections for the American people,” he said before the vote. “This is what they chose to make their top legislative priority this week. Taking an eraser to the First Amendment.”

The proposal, offered by Sen. Tom Udall (D-NM), would amend the Constitution to restore the authority of Congress to establish campaign finance limits, the kind that were axed in the 2010 Citizens United v. FEC and 2014 McCutcheon v. FEC Supreme Court rulings. According to a Senate Judiciary Committee report this year, it would also overturn part of the landmark 1976 Supreme Court ruling in Buckley v. Valeo, which upheld campaign contribution limits but invalidated restrictions on spending in elections.

“Since the decision came down in 2010, our campaign finance system has been under siege, buried in billions of dollars from outside groups and super PACs,” he said. “We have been fighting from day one to rid our political system of the poison of Citizens United. Folks want their senators to work together to find real solutions, not be bogged down in the endless gridlock of the Citizens United era.”

Progressive activists have waged a concerted campaign for the constitutional amendment, which they view as a long-term goal. Despite defeat in the Senate, they characterized the vote as a major step forward for the cause, saying that it shows that Americans are fighting back.

Clarification: This article has been updated to mention that the Udall amendment would also roll back part of a 1976 Supreme Court ruling, in addition to the more recent ones, on campaign finance.