WASHINGTON – Republican presidential candidate Mitt Romney has surged ahead of President Obama in fundraising for the first time, posing a fresh challenge for the incumbent amid political and economic headwinds that seriously threaten his chances of re-election.

Romney and the Republican National Committee said Thursday that they raised a combined $76.8 million in May, which is nearly as much money as the presumed nominee brought in during the entire GOP primary season. Obama and the Democratic National Committee brought in $60 million, which was their best month so far but still lagged behind their opponent, campaign officials said.

Romney’s monthly haul serves to undercut Obama’s reputation as the nation’s preeminent political fundraiser and signals growing confidence among Republicans that the former Massachusetts governor has a strong chance of defeating Obama.

The fundraising arms race has become one of the central features of the 2012 campaign, as each candidate criss-crosses the country for donor events on an almost daily basis. The presidential contest alone now appears likely to spur well over $2 billion in spending by campaigns, parties and interest groups.

“This is clearly an alarm,” said former Clinton administration aide Paul Begala, who advises a pro-Obama super PAC that has struggled to raise money from liberal donors. “I sure hope my Dems don’t hit the ‘snooze’ button. I have been saying for some time that this thing is far from in the bag. It’s not even in the shopping cart.”

RNC Chairman Reince Priebus said the May fundraising “is a sign that Americans are tired of President Obama’s broken promises and want a change of direction in the White House.” He vowed to “continue the hard work of raising the resources” to defeat Obama.

Obama campaign aides said they expected Romney to post strong fundraising numbers after clinching the Republican nomination in April, and maintain that the major financial threat to the president will come from conservative super PACs and other independent groups that can raise unlimited funds.

Jim Messina, Obama’s campaign manager, blasted out a fundraising email to supporters Thursday afternoon titled: “We got beat.”

Obama spokesman Ben LaBolt told reporters that “we knew this day would come,” noting that Democratic candidate John Kerry outraised incumbent president George W. Bush by 2-to-1 after clinching the party’s nomination in 2004.

“We anticipated that they would beat us this month,” LaBolt said. “We’re focusing on continuing to grow our donor base.”

Even with his strong May fundraising, Romney could still have difficulty catching up with Obama, who has been stockpiling cash for more than a year and building a massive infrastructure of campaign offices around the country. The Romney campaign and the RNC said they had $107 million cash on hand at the end of May; the Democrats, who did not release a cash estimate, had nearly $140 million cash on hand at the end of April between Obama and the DNC.

Asked about his fundraising haul Thursday, Romney said only: “Long way to go.”