Republican candidates, from left, Rick Santorum, Michele Bachmann, Newt Gingrich, Mitt Romney, Ron Paul, Tim Pawlenty and Herman Cain at their debate last month at St. Anselm College in Manchester, N.H. (Darren McCollester/Getty Images)

Are Republicans suffering from an enthusiasm gap?

After taking the House last November in a wave of conservative opposition to President Obama, Republicans now appear to be struggling to match the financial muscle of Democrats heading into the contentious 2012 elections.

The six GOP presidential candidates who have announced results raised a combined $35.6 million through June 30, including about $18 million by presumed front-runner Mitt Romney. In 2007, Republican candidates had raised more than $118 million by the same stage of the race, according to a new analysis from the Center for Responsive Politics.

The sluggish pace poses a serious complication in Republican efforts to unseat Obama, and suggests that GOP donors simply might be less enthusiastic than their Democratic rivals. The Obama campaign, which has not disclosed numbers, is expected to report raising at least $60 million — and perhaps as much as $80 million — in conjunction with the national party.

Republican strategists and donors attribute the depressed fundraising to a combination of factors, including a weak economy. But many GOP advisers also acknowledge that the numbers show a remarkable lack of excitement for the current Republican field, which includes two candidates — Romney and former Minnesota governor Tim Pawlenty — who have effectively been running for president since Obama was elected. Pawlenty in particular has struggled to raise money, finishing behind Rep. Ron Paul (R-Tex.) with $4.3 million.

Many wealthy GOP donors, meanwhile, have remained on the sidelines waiting to see whether another candidate such as Texas Gov. Rick Perry might enter the fray.

“Everyone is looking for Superman,” said Brian Ballard, a Florida donor who was a national finance co-chairman for the 2008 run of John McCain (Ariz.) but has not yet committed to any of the 2012 candidates. “I don’t think there is any other candidate who is going to come in and change the ultimate result, although Governor Perry could raise money.”

It is early in the election cycle, and things could change. Rep. Michele Bachmann (R-Minn.) is expected to report strong fundraising totals later this month based on her appeal among tea party voters. And a pro-Romney “super PAC” has raised $12 million in unlimited donations — money that will provide a de facto boost to his campaign.

Nonetheless, the disappointing GOP numbers come as welcome news for Democrats, who are bracing for an extremely difficult election amid persistently high unemployment and slow economic growth.

“It feels like they haven’t quite found a horse in this race,” said Jamal Simmons, a veteran aide to several Democratic presidential campaigns. “Romney is far ahead of his opponents, but he’s going to be lapped by all accounts by Obama.”

Obama advisers had vowed earlier to raise at least $60 million in combined fundraising with the Democratic National Committee in the second quarter, and the total is likely to go well beyond that amount. The campaign says it took in more than 480,000 contributions overall, more than twice the number as four years ago.

Richard L. Hasen, a campaign-finance expert at the University of California at Irvine, said economics can’t fully account for the GOP woes. “If Obama’s numbers are good, that would tend to suggest the downturn explanation is less important than an enthusiasm gap,” he said.

Top Republicans insist that party activists are excited about the prospect of defeating Obama. And one Romney campaign aide said, “We are very pleased with the total” raised.

Other Republicans note that the contest has developed far more slowly than in 2007, when several candidates were running full-blown campaigns by March.

“We are probably at least six months behind where we were in 2007,” said Saul Anuzis, the former chairman of the Michigan Republican Party. “Our nominating process is very conservative and not just in the political sense. We are methodical and slow-moving in that respect.”

Longtime GOP donor Fred Malek, who is sitting on the sidelines in the presidential race to raise money for the Republican Governors Association, agreed: “A lot of people are waiting to see a complete field, and I think that’s completely understandable.”

Both Romney and Pawlenty have long been meeting with potential bundlers in anticipation of White House runs. Romney has been courting the party’s major donors now for more than half a decade. By this time in 2007, he had raised nearly $38 million from donors, more than twice his current figure.

Some strategists said the new super PACs — which provide a vehicle for wealthy donors to spend an unlimited amount of money — might also be siphoning support from traditional campaigns.

“A lot of typically big-dollar GOP funders, rather than donating to a candidate, are giving money to the new super PACs where they can give big dollars . . . and not get burned by being with the wrong candidate,” said Mark McKinnon, a GOP strategist and former McCain adviser. “Later, they can give to the nominee once there is one.”