WASHINGTON - Mitt Romney and his Republican Party raised $40 million in April, an unexpectedly strong haul in the first month of the general campaign that illustrates enthusiasm within the GOP and threatens President Obama's overwhelming cash advantage.

Since becoming the presumptive Republican presidential nominee, Romney has devoted most of his time to privately courting donors so he can prepare for what may be the most expensive campaign in history. His focus appears to be paying off. In just one month, Obama's 10-1 cash advantage has shrunk to 2-1, partly because the Republican National Committee now is helping Romney.

Romney's April fund-raising figures - a sharp increase from March, when he pulled in just $12.5 million while fending off primary opponents - show that he and the RNC together raised nearly as much money as the president and the Democratic National Committee, which together brought in $43.6 million last month.

Romney's new numbers don't reflect millions of dollars more raised and spent by pro-Romney super PACs.

Full financial reports aren't due to the Federal Election Commission until midnight Sunday. The filings will detail the names and personal information for all donors, providing new insight on the sources of each campaign's cash.

The reports will do little to shed light on spending by outside groups.

Earlier this week, the independent group Crossroads GPS announced a $25 million, monthlong advertising blitz against Obama in 10 states. The ad push is the latest to illustrate the degree to which the campaign is playing out under dramatically looser campaign-finance laws after a series of Supreme Court decisions allowed independent groups to raise and spend unlimited sums as long as they don't coordinate directly with the campaigns they support.

The super PAC Restore Our Future, staffed with former Romney aides, has spent at least $4.3 million so far, while Americans for Prosperity, the group founded by brothers Charles and David Koch, has spent $5 million. The American Future Fund, whose goal is to promote conservative and free-market ideas, is spending an additional $4.7 million to run a one-minute ad suggesting Obama hasn't cracked down on Wall Street because of his campaign's fund-raising.

Pro-Obama super PACs haven't brought in nearly what their counterparts on the right have, though one - Priorities USA Action - is spending $4 million to air ads attacking Romney.