When the votes were counted, President Obama's campaign declared victory over the conservative "super PACs" that had sought to bury him in negative ads and win the White House and the Senate for the Republican Party.
Though the outcome of the 2012 elections dealt a blow to the wealthy donors who poured several hundred million dollars into groups seeking to defeat Mr. Obama, the president's re-election does not presage a repudiation of the deregulated campaign financing unleashed by the Supreme Court's 2010 Citizens United decision. Instead, his victory most likely reinforced the practice.
In virtually every respect, the growth of unlimited fund-raising and the move of outside groups to the mainstream of politics have magnified the already outsize role of money in political campaigns. They have changed how incumbents and challengers alike campaign and raise money, altered how voters experience politics, and expanded the influence of a small group of large donors on the policies and messages espoused by candidates.
Mr. Obama, who has denounced Citizens United and the wave of outside spending it helped create, once hoped to win re-election the old-fashioned way, relying on money he raised for his campaign and the Democratic Party.
But ultimately, Mr. Obama did not beat the super PACs; he joined them. When Priorities USA Action, a super PAC started by two former White House aides, foundered, the president dispatched high-ranking campaign and administration officials around the country, where they beseeched small groups of millionaires and billionaires to contribute large checks. Fund-raising picked up, and by Election Day, Priorities USA Action had spent $66.5 million on attack ads, much of it paid for by a small group of investors, trial lawyers and labor unions.
That spending — along with tens of millions of dollars in pro-Obama spending by other super PACs and outside groups — substantially evened the score against Republicans and their allies. During the general election campaign, the net advantage in outside spending by conservative groups over pro-Obama outside groups shrank to $200 million, about 10 percent of all spending in this presidential race.
Congressional Democrats embarked on a similar arms race. Allies of the Democratic leadership founded semiofficial super PACs with the goal — mostly successful — of narrowing the Republicans' edge in outside spending enough to be financially competitive. Liberal donors, once skeptical of outside spending and philosophically opposed to super PACs, provided the money, making both parties participants in the unlimited fund-raising.
Mr. Obama also helped undermine one of the vestiges of the post-Watergate campaign reforms: public financing for the general election. His decision not to accept public financing and its restrictions in 2012, as he had in 2008, prompted Mitt Romney to do the same. As a result, the political fund-raising season — which once drew to an end when exhausted donors and fund-raisers arrived at high-end hotels for each party's convention — continued nearly through Election Day.
By the week of the election, according to tallies by CBS News, Mr. Obama had attended 221 fund-raisers, far more than any other incumbent president, in 24 states, Washington and Puerto Rico. During the same period, he attended 101 campaign rallies in 9 states.
Explaining the drive for cash, Mr. Obama's campaign again and again cited the threat from spending by conservative outside groups.
For long stretches of the summer and fall, Mr. Romney was so busy with fund-raisers that he often did no more than one public event a day. Incumbents in Congress, some of whom faced millions of dollars in last-minute ads against them from super PACs and other groups, are also under pressure in the post-Citizens United world to spend even more time raising money.
In recent weeks, some Republicans have suggested lifting caps on contributions to candidates, a shift that would abolish the only other vestige of the post-Watergate reforms.
"It opens the floodgates even more," said Representative Chris Van Hollen of Maryland, a Democrat who has pushed for more disclosure and limits on outside spending. "I don't think it's good for the process for people to have to spend even more time raising money to have an insurance policy against super PACs."
Some strategists in both parties said they believed that the central role of super PACs in the Republican primaries will make it difficult for candidates in 2016 — when both parties will have contested primaries — to resist deploying allies to organize one, forcing them to compete for the allegiance of a small group of wealthy donors who can write six- and seven-figure checks.
Restore Our Future, a super PAC formed by former aides to Mr. Romney, spent more than $40 million — most of it raised from a few dozen wealthy donors — to ensure Mr. Romney's nomination, significantly more money than any of his rivals raised.
Mr. Romney's leading rival for much of the primary season, Newt Gingrich, was able to compete only with the help of a large super PAC working in his behalf. It raised more than $20 million from a single family: that of the casino billionaire Sheldon Adelson, whose hawkish views on Israel both Mr. Gingrich and Mr. Romney supported. Rick Santorum also had the support of a super PAC, allowing him to stay in the race and lengthen the battle for the nomination in the Republican primaries.
Thanks to super PACs, "a Newt Gingrich or a Rick Santorum and their followers were able to have their voices heard and their views more widely distributed," said Bradley A. Smith, chairman of the Center for Competitive Politics, which favors less regulation of campaign money.
The 2012 election was without question also a triumph of the very small donor, millions of whom accounted for about 56 percent of Mr. Obama's fund-raising.
That money helped Mr. Obama pay for most of his advertising himself, a major advantage under federal rules that require television stations to give candidates preferential rates on advertising. Mr. Romney, who was more dependent on money controlled by the Republican National Committee and outside groups, effectively outsourced his advertising campaign, meaning he got less for his dollar.
In the end, the president and his allies appear to have matched or exceeded Mr. Romney and his allies in the number of advertisements that aired. Warnings from liberals and advocates of tighter campaign finance regulation that outside conservative money would swamp Mr. Obama proved incorrect, if only because the White House and its allies exploited the new rules of the game as well as, and maybe much better than, Republicans and their allies did.
Yet Mr. Obama's grass-roots money success sets a high bar. No other candidate in history has built anything like his base of small donors. Only a few other candidates of either party are likely to be able to match it; those who cannot in 2016 may have to face off against super PACs without the money and flexibility that Mr. Obama's four million small donors provided.
"If the Democratic Party is smart, they are going to try to preserve the structure of what Obama did and keep it going," said Rick Hasen, a professor of law and political science at the University of California, Irvine, and an expert on voting and campaign finance. "If Republicans are smart, they are going to try to replicate it."