WASHINGTON — The Supreme Court on Wednesday further opened up the taps on political campaign spending, with a bombshell ruling that removes the longstanding limits on how much total money an individual can contribute to federal candidates.

In what amounts to a 5-4 ruling won by conservatives, the court declared the aggregate contribution limits imposed four decades ago violated the First Amendment’s free-speech protections. Though individual donations may still be limited, for now, the ruling means donors can spread their wealth across as many candidates and causes as they can find.

“They … intrude without justification on a citizen’s ability to exercise the most fundamental First Amendment activities,” Chief Justice John Roberts Jr. wrote of the aggregate contribution limits.

Roberts’ 40-page opinion, joined by three other conservative justices, continues the court’s dismantling of congressional campaign finance reform efforts, including landmarks laws passed in 1974 and 2002, and its constitutional reasoning leaves remaining campaign restrictions at risk. Justice Clarence Thomas joined the conclusion, making an effective 5-4 majority, though he wrote a separate concurring opinion calling for the end of other campaign limits as well.

The court’s four Democratic appointees dissented.

“It understates the importance of protecting the political integrity of our governmental institutions,” Justice Stephen Breyer wrote of the conservative majority’s opinion. “It creates a loophole that will allow a single individual to contribute millions of dollars to a political party or to a candidate’s campaign.”

A 1974 campaign finance law, enacted in the wake of the Watergate political scandal, imposed several kinds of restrictions. Limits were placed on how much an individual or committee could give a particular candidate. Aggregate limits were also set, capping the total that a donor might contribute to all candidates and committees.

The ruling Wednesday covers the aggregate limits, which currently restrict an individual to giving $123,200 to candidates and parties over a two-year election cycle. Of this total, an individual can give up to $48,600 to federal candidates and their campaign committees and up to $74,600 to political parties and non-candidate committees.

The limits are adjusted every two years for inflation.

“We have made clear that Congress may not regulate contributions simply to reduce the amount of money in politics, or to restrict the political participation of some in order to enhance the relative influence of others,” Roberts wrote.

Alabama businessman and Republican donor Shaun McCutcheon challenged the Federal Election Commission. During the 2011-2012 election campaign, he donated a total of $33,088 to 16 different federal candidates. He says he wanted to donate to another 12 candidates as well, but his intended donations would have exceeded the aggregate limit. He also says he wanted to boost his contributions to federal Republican committees, but again ran into the aggregate limit.

Federal candidates, parties and committees reported raising and spending more than $7 billion during 2011 and 2012, according to the Federal Election Commission.

In the 2010 case known as Citizens United, conservatives aggressively expanded a limited case to broadly rule against limits on corporation and labor union spending

In a 1976 decision, called Buckley v. Valeo, the Supreme Court upheld much of the 1974 law and divined a difference between campaign donations and campaign spending. Spending by a candidate was deemed tantamount to political speech, and so received greater First Amendment protection. Campaign donations to the candidate were deemed potentially corrupting and hence subject to regulation.