Never before has so much political money been spent to achieve so little.

Record spending by independent groups, which in many ways defined how campaigns were waged this year, had no dis­cern­ible effect on the outcome of most races, according to an analysis by The Washington Post.

A clutch of billionaires and privately held corporations fueled more than $1 billion in spending by super PACs and nonprofits, unleashing a wave of attack ads un­rivaled in U.S. history. Yet Republican groups, which dominated their opponents, failed to achieve their two overarching goals: unseating President Obama and returning the Senate to GOP control.

In the Senate, Republicans lost ground, after pouring well over $100 million in outside money into seven races that went to Democrats. In the presidential race, GOP nominee Mitt Romney nearly matched Obama with the help of outside money, yet he lost decisively in the end.

Even in the House, which remains comfortably in Republican hands, GOP money groups struck out repeatedly in individual races they targeted, according to the Post analysis of data from the Center for Responsive Politics. In 24 of the most competitive House contests, Democratic candidates and their allies were outspent in the final months but pulled out victories anyway. That compares with eight competitive races in which Republicans were outspent and won.

Spending by outside groups, it turns out, was the dog that barked but did not bite. Obama and other Democrats had long made dire predictions about the potential impact of the Supreme Court’s 2010 decision in Citizens United v. Federal Election Commission, which allowed corporations and unions to spend unlimited money on elections and created a new class of wealthy political groups.

The money clearly did change the focus and tenor of many campaigns. Candidates up and down the ballot were forced to spend more time seeking donations, while political ads funded by outsiders gave a profoundly negative shine to many contests.

Wealthy donors were so central to Romney’s campaign that a swarm of private luxury jets caused a traffic jam at Boston’s airport Tuesday just before the nominee’s election-night party.

But conservative super PACs and secretive nonprofit groups — which spent up to $10 million a day on the presidential race alone — couldn’t move the needle far enough to prevail in almost any of the major races they targeted. Romney’s reliance on outside money also gave him less control over spending, while his campaign was plagued by high personnel costs and lavish consulting fees.

If either Romney or Obama had held a substantial cash advantage, it is possible that one candidate could have dominated in the final weeks of the campaign. But the two camps were roughly evenly matched by the end. The result was a kind of dreary equilibrium, as both sides clogged the airwaves with so many attack ads that Republicans began airing spots in California and other deep-blue states.

By the end of October, more than 1 million commercials had been broadcast in a presidential race that stayed close to a tie for much of the year.

Bad investments

Indeed, if election investments are like the stock market, a lot of billionaires just lost their shirts. American Crossroads, co-founded by GOP political guru Karl Rove, and Restore Our Future, which focused on supporting Romney in the presidential race, together spent more than $450 million, with little to show for it in the end. The groups relied on six- and seven-figure checks from energy executives, hedge-fund managers and other wealthy donors eager to oust Obama and congressional Democrats.

The most generous donors of all, Las Vegas casino magnate Sheldon Adelson and his wife, Miriam, funneled more than $53 million to groups backing Romney, GOP primary hopeful Newt Gingrich and other Republicans. Nearly every one of them lost on Tuesday, from House candidate Shmuley Boteach in New Jersey to Senate candidates Richard Mourdock in Indiana, Connie Mack in Florida and Josh Mandel in Ohio.

“I think it shows that it’s not always about the money,” said Rodell Mollineau of American Bridge 21st Century, a small super PAC that spearheaded opposition research efforts for Democrats.

That’s not to say that outside money didn’t matter. Obama and congressional Democrats were helped mightily by super PACs, environmental groups and unions, while Romney gained the GOP nomination with the help of $55 million in attack ads from Restore Our Future.

“I think it’s indisputable that we were incredibly effective and important in the primary,” said Charlie Spies, a co-founder of the group, which spent an additional $100 million or so helping Romney after he secured the nomination.

Spies said the super PAC was the first to spend in Wisconsin and Michigan, forcing the Obama campaign to move ad dollars into those states. Restore Our Future also bolstered Romney’s advertising at critical periods when his campaign was short of money, Spies said.

The $1 billion candidate

Romney the candidate was the strongest Republican fundraiser ever, but he was still no match for Obama, who raised more than $1 billion in contributions — about half from donors giving $200 or less at a time. Romney’s campaign relied primarily on wealthy donors and conservative groups to help make up the difference.

“GOP super PACs leveled the playing field,” said Jonathan Collegio, a spokesman for American Crossroads and its nonprofit affiliate, Crossroads GPS, which together spent about $300 million to help Romney and other Republicans.

More than 250 groups spent $100,000 or more on the elections, according to Center for Responsive Politics data, mostly super PACs focused on one candidate or cause. The deluge fueled a campaign arms race of sorts, as candidates in both parties increasingly focused on raising as much cash as possible for fear of what the other side had in store.

Obama held more than twice as many fundraisers as rallies during the long campaign; Romney’s running mate, Rep. Paul Ryan (Wis.), was still seeking money in red states two weeks before Election Day.

The outside groups Republicans depended on were hampered by laws that give favorable ad rates to candidates, meaning these groups generally paid higher prices. Even at the end, when Romney and his allies began outspending Obama on the airwaves, the incumbent still ran more commercials in most swing-state markets.

In the Senate, the conservative push was a resounding failure. Crossroads, the U.S. Chamber of Commerce and other GOP-leaning groups spent at least $94 million targeting Democrats Tammy Baldwin (Wis.), Sherrod Brown (Ohio), Joe Donnelly (Ind.), Heidi Heitkamp (N.D.), Timothy M. Kaine (Va.), Bill Nelson (Fla.) and Jon Tester (Mont.), according to FEC data; all emerged victorious Tuesday.

“Our victory proves neither corporations nor billionaires can buy Montana,” Tester said after his race was declared on Wednesday.

The Sunlight Foundation, which tracks money in politics, calculated Wednesday that two-thirds of the money spent by outside groups backed losing candidates. Success rates varied dramatically from group to group: American Crossroads and its nonprofit affiliate spent about 6 percent of their funds on winners, while the Service Employees International Union had a 70 percent victory rate, Sunlight found.

Several Republicans were widely seen as flawed candidates who probably couldn’t have been saved. Mourdock — who defeated longtime Sen. Richard G. Lugar in Indiana’s GOP primary with the help of super PACs — hurt his chances when he said that if a woman becomes pregnant as a result of rape, it is something “God intended to happen.” Republican groups outspent Democrats 2 to 1 in the race, yet Donnelly trounced Mourdock by six points.

Senate spending

The single most expensive congressional race was the Senate contest in Virginia between Kaine and George Allen (R), which attracted more than $50 million from independent groups; Kaine won comfortably. In Connecticut, former wrestling company executive Linda McMahon (R) failed in her second try at the Senate, having spent more than $90 million of her fortune over two races.

One matchup largely untouched by outside spending was in Massachusetts, where Democratic challenger Elizabeth Warren bested Sen. Scott Brown (R). The candidates had agreed to discourage third-party groups from running ads; the pact ended up benefiting Warren, who raised more money than her opponent.

In the House, Rep. Robert J. Dold (R) of Illinois fell to Democrat Brad Schneider despite $1.9 million spent by Republican groups in the final weeks of the campaign, compared with just $5,600 in outside help for Schneider.

Democrats beat three other Republican incumbents in Illinois, despite being outspent in each race. In the starkest example, GOP groups had spent $5.3 million since Sept. 1 to try to save Rep. Joe Walsh, but he lost to Tammy Duckworth, an Iraq war veteran and former Obama appointee who received $454,000 in outside help.

Many targeted candidates in both parties complained that super-PAC money distorted their races and forced them to spend valuable time seeking money and mounting a defense rather than discussing issues.

In Oregon, Rep. Peter A. DeFazio (D) came under attack for a second cycle from a super PAC funded by a New York hedge-fund manager who opposes a financial transactions tax sponsored by the incumbent. The group spent $500,000 against him, most of it in the final two weeks; DeFazio won easily on Tuesday.

“He’s putting everything he’s got against me,” DeFazio said before the election. “It’s no walk in the park, that’s for sure.”