The most expensive election in American history drew to a close this week with a price tag estimated at more than $6 billion, propelled by legal and regulatory decisions that allowed wealthy donors to pour record amounts of cash into races around the country.

But while outside spending affected the election in innumerable ways — reshaping the Republican presidential nominating contest, clogging the airwaves with unprecedented amounts of negative advertising and shoring up embattled Republican incumbents in the House — the prizes most sought by the emerging class of megadonors remained outside their grasp. President Obama will return to the White House in January, and the Democrats have strengthened their lock on the Senate.