Senate Republicans successfully blocked a constitutional amendment backed by Democrats that would have allowed Congress to place limits on campaign spending.

The measure, which the GOP unanimously rejected on Thursday, would have granted Congress the ability to regulate campaign finance reform. As a result, the 54-42 vote failed to clear the 60-vote threshold after days of heated debate.

Senate Majority Leader Harry Reid, a Democrat from Nevada, bashed Republicans for blocking the amendment due to their ties to wealthy conservative supporters like the billionaire Koch brothers.

"Senate Democrats want a government that works for all Americans -- not just the richest few. Today, Senate Republicans clearly showed that they would rather sideline hardworking families in order to protect the Koch brothers and other radical interests that are working to fix our elections and buy our democracy," Reid said after the vote, according to Politico.

The constitutional amendment, dubbed the Democracy for All Amendment, would allow Congress and state lawmakers to override the Supreme Court's decision in Citizens United, which struck down campaign finance laws in 2010, reports the Washington Post.

However, Republicans argued that the amendment would have put a damper on free political speech, which is protected under the First Amendment.

"The proposed amendment would restrict the most important speech the First Amendment protects, core political speech," Republican Sen. Chuck Grassley said on Wednesday. "It's hard to imagine what would be more radical than the Congress passing a constitutional amendment to overturn a dozen Supreme Court decisions that have protected individual rights. Free speech would be dramatically curtailed."

Although it was unlikely that Senate Democrats would have succeed in passing the constitutional amendment, Democrats capitalized on the opportunity to highly massive political spending by billionaires.

Left-leaning groups like American Civil Liberties Union (ACLU) and Public Citizen offered opposing opinions on the issue.

The ACLU maintained its opposition to laws prohibiting anyone from speaking about political issues.

"Any rule that requires the government to determine what political speech is legitimate and how much political speech is appropriate is difficult to reconcile with the First Amendment. Our system of free expression is built on the premise that the people get to decide what speech they want to hear; it is not the role of the government to make that decision for them," the ACLU saod, according to Forbes.

On the other hand, Public Citizen backed Sen. Tom Udall's constitutional amendment that would allow limits on "the amount of funds that may be spent by, in support of, or in opposition to" state and federal candidates.