Las Vegas Sands chief executive Sheldon Adelson and his wife, Miriam, attend the first presidential debate at Hofstra University in Hempstead, N.Y., on Sept. 26. (Paul J. Richards/AFP/Getty Images)

Super PACs seeking to influence the 2016 elections have collected more than $1 billion, a record haul driven by jumbo-sized contributions from rich donors on both sides of the aisle.

Just 10 mega-donor individuals and couples contributed nearly 20 percent of the $1.1 billion raised by super PACs by the end of August, according to a Washington Post analysis of federal campaign finance reports. The total exceeds the $853 million that super PACs collected in the entire 2012 cycle.

In a reflection of how once-reluctant Democrats have fully embraced the big-money system, the top givers were split roughly equally along party lines, with five Republicans, four Democrats and one independent, former New York mayor Michael Bloomberg.

On the left, large check writers have pumped millions into Priorities USA Action, the top super PAC allied with Democratic presidential nominee Hillary Clinton, who has struggled to demonstrate her independence from her wealthy supporters.

On the Republican side, the big money has largely flowed into super PACs working to keep GOP control of the Senate rather than to the muddled collection of competing groups supporting presidential nominee Donald Trump.

Here's what a super PAC can (and can't) legally do. (Sarah Parnass/The Washington Post)

Together, super PACs seeking to sway the White House and congressional races have pumped more than $674 million into TV ads and other outreach through September, filings show. By the end of the 2012 elections, such groups had spent $608 million.

The figures illustrate how American campaigns have been reordered by the ability to give unlimited sums to political committees. In the six years since the Supreme Court’s Citizens United v. Federal Election Commission decision created new paths for massive contributions to flow into elections, a tiny sliver of donors with immense financial capacity have rushed to participate.

Along with the $1.1 billion raised by super PACs, hundreds of millions more has been directed into politically active nonprofits on both sides of the aisle that can keep the names of their contributors secret.

The huge sums washing through campaigns are contributing to a growing estrangement between voters and the political system, critics said.

“The big picture is that it just continues to rest the political system on the wallets of the wealthiest Americans, and that defies the basic American belief in ‘we the people,’ ” said Nick Penniman, executive director of ­Issue One, a bipartisan group working to reduce the influence of wealthy interests on politics. “If you’re a regular voter and you felt less relevant in the political system 10 years ago, you feel even less relevant today.”

[Meet the wealthy donors who are pouring millions into the 2016 elections]

There are already signs that more waves of cash are coming before Election Day. Casino mogul Sheldon Adelson and his wife, Miriam — who jumped in late this year, giving $21.5 million in August to GOP super PACs defending Senate candidates — are directing millions into a group that has launched a new anti-Clinton effort.

And hedge fund founder Tom Steyer, who had given $38 million through August to groups working to mobilize young voters, Latinos and union members, said last month that he was putting in at least $15 million more.

In an interview with The Post, the billionaire environmentalist — who ranks as the biggest super PAC donor of the cycle so far — called Citizens United a “terrible decision.” And he said he agrees with those who believe “money is corrupting our politics.”

“I think it’s actually a significant threat to our democracy if our citizens don’t believe that our democracy is fair and it plays to special interests,” Steyer said.

But he said he was shelling out massive sums because “the other side is going always to have a ton more money than us.”

“This is the system we have, and we’re trying to participate as transparently as we can within that system,” Steyer said.

[Hillary Clinton’s main super PAC has raised $132 million. A third came from six wealthy allies.]

In second place on the top donor list through August was another hedge fund founder, Donald Sussman, who has plowed more than $23 million into groups allied with Hillary Clinton and other Democratic candidates.

The Adelsons were in third place, followed by conservative billionaire Robert Mercer, who has given $20.2 million so far, largely to back Sen. Ted Cruz of Texas in the GOP presidential primaries. Since Cruz bowed out, Mercer and one of his daughters, Rebekah, have emerged as the most dominant donors in Trump’s orbit.

Bloomberg, the billionaire media mogul, was in fifth place, with $20.1 million, most of which went to his super PAC, Independence USA, which is backing GOP Sen. Patrick J. Toomey in Pennsylvania and Democratic Senate contender Maggie Hassan in New Hampshire.

Rounding out the top 10 list were Chicago media company owner and Democratic donor Fred Eychaner ($20 million), conservative hedge fund executive Paul Singer ($17.3 million), liberal investor George Soros ($16.5 million), former AIG head and Republican financier Maurice “Hank” Greenberg ($15.1 million) and conservative shipping magnates Elizabeth and Richard Uihlein ($14 million).

David Keating, the conservative activist who launched the federal appellate case that created super PACs, said he is not surprised by the size of the contributions flowing to the groups, which can accept unlimited amounts from both individuals and corporations.

And he noted that money is no guarantee of success, pointing out that former Florida governor Jeb Bush’s presidential bid fizzled, despite the backing of a well-funded super PAC.

“I think people have to keep in mind that it’s just speech, it’s just communications,” Keating said. “As we saw earlier in the year with Jeb Bush, spending money on speech doesn’t equal having a candidate you back win an election. You can talk to people, but you can’t make them agree with what you’re talking about.”

“The alternative,” he added, “is the government saying, ‘You can’t do this.’ That to me is a much scarier prospect.”

One of the biggest beneficiaries of the current system has been Clinton. Even as she has been touting her support for a reversal of the Citizens United decision on the campaign trail, her top allied super PAC, Priorities USA Action, has raised nearly $132 million — on track to more than double what the group pulled in when it backed President Obama’s reelection in 2012.

“We fully support Hillary Clinton’s call for campaign finance reform, and until then it’s the height of hypocrisy that Republicans would attack Democrats for not fighting with one hand tied behind their back,” said spokesman Justin Barasky.

[Here comes the Republican Senate super PAC blitz]

On the Republican side, a large share of the funds in the general election has flowed to the Senate Leadership Fund, a super PAC that is part of the American Crossroads suite of GOP big-money groups.

Steven Law, the super PAC’s president and a former chief of staff to Senate Majority Leader Mitch McConnell (R-Ky.), said donors have flocked to protect the Senate majority because they see the fight as a “concrete, achievable goal.” Big givers believe outside spending can have a clear impact on those campaigns, unlike in the White House race, which is “much larger, more chaotic and harder to predict,” he added.

The Adelsons and TD Ameritrade founder Joe Ricketts have indicated that they plan a late burst of spending on Trump’s behalf, but an assortment of super PACs that have sought to back Trump’s candidacy have struggled to raise funds.

That’s largely because of the mixed signals sent by Trump, who denounced super PACs in the primaries. Since securing the nomination, his top advisers have suggested he was open to their support, but they have not made it clear which group they favor.

“It has been very frustrating, and unnecessarily so,” said Doug Watts, the national executive director of the pro-Trump Committee for American Sovereignty super PAC. He said a donor backed out of a $100,000 pledge last week because of concern that the candidate did not approve of the big-money groups.

“In past years, I think super PACs were a luxury,” Watts said. “This year, I think they were a necessity.”