Outside groups, including super PACs and nonprofit organizations, have spent almost four times more on the 2012 presidential campaign than comparable organizations spent at the same point in the 2008 cycle, an analysis of Federal Election Commission filings show.

Four years ago in late March, when Republicans had already wrapped up a wide-open battle for their party's nomination and Democrats were still engaged in a battle that would go on for months, spending on the presidential campaign by independent groups stood just shy of $22 million. Today, outside spending on the race for the White House has already topped ...