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.