Barack Obama and Hillary Clinton have spent $121 million combined vying for the Democratic presidential nomination, swamping the $57 million spent by all Republican presidential candidates through the primary season.

Obama spent nearly $75 million on television ads, while Clinton bought $46 million worth of spots to date, according to the Joyce Foundation’s Wisconsin Advertising Project.

Republican John McCain, who essentially secured his party’s nomination in March, has spent a paltry $11 million on 16,413 airings of his ads. More than half of the GOP’s ad dollars were spent by Mitt Romney, who dropped out of the race in February. The Wisconsin Advertising Project calculated Romney spent $31 million boosting his failed candidacy.

All in all, the 2008 presidential candidates have spent nearly $195 million promoting their campaigns. Democratic advertising made up the bulk of the spending at $135 million, while GOP candidates spent some $57 million combined.

Clinton, forced to lend her campaign personal money at two different points during the primary season, was able to put up 80,505 airings of her television ads. Obama’s $75 million bought 139,000 airings. In the run-up to February 5, “Super Tuesday,” Clinton and Obama spent roughly the same amount of money on ads. Then, Obama upped his advertising budget. From Super Tuesday through February 19 Obama’s ad spending outpaced Clinton’s by a 3-1 ratio. During that streak Obama won nine straight primaries and gained 281 delegates to Clinton’s 163.

The Wisconsin Project’s study said “the advertising advantage alone, of course, does not explain Obama’s victories in these contests,” but notes “in the nine states that Obama won in a two week period following the February 5 Super Tuesday primaries, Obama, not only had an advantage in the number of ads that he aired, but in most of the nine contests, he was also first on the air and had the paid media airways all to himself for a significant part of the short campaigns. For example, in Nebraska, during the short nine-day advertising war, Obama was up alone, with his messages not countered for six days.” Obama was “up alone” in Wisconsin for six days, and in Maryland and Virginia he ruled the airwaves for 7 out of the 12 days of intense campaigning against Clinton.

Special interest groups supplemented Obama’s spending. The Service Employees International Union has purchased more than $2 million worth of ads to benefit Obama’s candidacy. This number includes an $800,000 negative ad campaign against McCain. Likewise, the liberal advocacy group MoveOn.org and the environmental lobbying group Friends of the Earth has spent $373,000 and $138,000 attacking McCain, respectively.

University of Wisconsin’s Ken Goldstein, who headed up the story, thinks McCain got off easy. “A big story in this campaign is the hundreds of millions that were not spent attacking John McCain in February, March, April and now May of 2008,” he said in a statement to publicize his findings. He said the Democrats may regret their failure to spend significant amounts of money opposing McCain and building up their party in November. “By any reasonable measure, the Democrats should win the presidency and strengthen their control of Congress,” Goldstein said. “If they do not, the money that was not spent early to define John McCain among voters in swing stats and to strengthen Democratic congressional candidates this spring may be one of the reasons.”

For all the money that has been spent by Clinton and Obama neither of them has been named the Democratic nominee. The Democratic primary will finally come to a close on when Montana and South Dakota hold their contests Tuesday. Obama is expected to secure the nomination outright, by way of delegates won from those states and party “superdelegates” who will endorse him after the primaries conclude. Clinton, however, is threatening to challenge party rules and possibly extend the nomination fight, and the Democratic battle for airwaves, until August.