The Supreme Court has struck down a key remaining pillar of campaign finance law, handing a big victory to the Republican Party. And now there’s concern the court could soon go even further.

By a 5-4 ruling, the court decided that aggregate limits on campaign contributions—that is, how much an individual can give in total contributions per cycle—are an unconstitutional violation of the First Amendment’s guarantee of free speech.

The Justices did not touch the more prominent limits on how much an individual can give to any single camapign or committee. But many campaign finance experts say the ruling suggests that those limits could be the next to fall.

Close video First Read: Supreme money The Supreme Court just rewrote the rules for financing elections, pushing political parties and candidates to devote their time to securing the country’s richest donors. Chuck Todd reports on the winners and losers of the McCutcheon v. FEC ruling with… The Supreme Court just rewrote the rules for financing elections, pushing political parties and candidates to devote their time to securing the country’s richest donors. Chuck Todd reports on the winners and losers of the McCutcheon v. FEC ruling with… share tweet email Embed

Justice Clarence Thomas wrote his own opinion in which he argued for scrapping those limits. None of the other Justices joined him. But the court did say that campaign finance laws can only aim to stop quid pro quo corruption, not less direct forms of corruption. In doing so, the court may have laid the foundation for a fresh challenge to the individual limits, based on the argument that they define corruption too broadly and aren’t narrowly tailored to stop quid pro quo corruption.

Senate Minority Leader Mitch McConnell argued in an amicus brief that the individual limits should be struck down. And David Donnelly of Public Campaign Action Fund said McConnell may get another chance to make his case.

“That is the last remaining piece of our election law,” Donnelly said,. “Clearly that’s going to be the next effort.”

Wednesday’s ruling is plenty far-reaching on its own. The court found that the only kind of corruption the government can legitimately use campaign finance laws to address is quid pro quo corruption, and that the aggregate limits do not further that goal. Instead, wrote Chief Justice John Roberts for the majority, they “intrude without justification on a citizen’s ability to exercise ‘the most fundamental First Amendment activities.’”

The court’s five conservative justices struck down the limits, while the four liberal justices dissented.

“With its Citizens United and McCutcheon decisions, the Supreme Court has turned our representative system of government into a sandbox for America’s billionaires and millionaires to play in,” said Fred Wertheimer, a veteran Washington campaign finance advocate.

Close video SCOTUS rejects campaign contribution limits The Supreme Court struck down major law that limited contributions to federal political campaigns. NBC’s Pete Williams discusses the latest with Chris Jansing. The Supreme Court struck down major law that limited contributions to federal political campaigns. NBC’s Pete Williams discusses the latest with Chris Jansing. share tweet email Embed heavy backing from the GOP. McCutcheon had already contributed to 16 Republican candidates, but wanted to give to 12 more, and to give separate $25,000 contributions to three Republican committees. Doing so would have put him over the aggregate limits.

Here’s how the ruling could have a major impact: It will allow politicians to solicit multimillion-dollar contributions from wealthy backers, then disburse that money to different campaigns. So the money wouldn’t all go to one candidate—in a small piece of good news for campaign finance advocates, the court didn’t touch the limits on individual contributions – but the donor would still be able to buy millions of dollars worth of influence.

“If you’re John Boehner, you can set up a joint fundraising committee with your 218 members of the House, or candidates in even more races,” explained Donnelly. “And you can raise a single contribution through that joint fundraising committee of millions of dollars, and then just distribute the money through that joint fundraising committee to the different candidates.”

“You all have the freedom to write what you want to write, donors ought to have the freedom to give what they want to give,” Boehner told reporters after a meeting of House Republicans Wednesday morning.

The reaction to the ruling from progressives was swift. “The Roberts Court has doubled down on Citizens United – striking down some of the last remaining limits on how much wealthy donors can spend on elections,” said the Progressive Change Campaign Committee, as it launched an online ad denouncing the ruling. “With those limits gone, it will be even harder for everyday people to have their voices heard in Washington.”

But conservatives cheered the ruling.

“This is a great day for the first amendment, and a great day for political speech,” said Club for Growth president Chris Chocola in a statement. “With Citizens United and now McCutcheon, the Supreme Court has continued to restrict the role of the federal government in limiting and regulating speech. We hope further efforts to increase the ability of citizens to participate in our democracy are also successful.”