WASHINGTON — Record spending by independent groups largely defined how the 2012 elections were fought, but the money had no discernible impact on the outcome of most contests, according to an early analysis of ballot results and expenditures by the Washington Post.

A clutch of conservative billionaires and privately held corporations fueled about $1 billion in spending by super PACs and nonprofit groups this cycle, unleashing a wave of attack ads unrivaled in US history. Yet Republican groups and their donors failed to achieve their two overarching goals — to unseat President Obama and return the Senate to GOP control.