This photo combo shows President Barack Obama in Chapel Hill, N.C. on April 24, 2012, and Republican presidential candidate, former Massachusetts Gov. Mitt Romney on April 18, 2012 in Charlotte, N.C. Obama and his likely GOP opponent, Romney, agree on an issue of importance to college students: Keeping the interest rate low on a popular federally subsidized student loan issued to low-and middle-income students. (AP Photo)

WASHINGTON (AP) -- Independent Republican groups are heavily outspending their cross-party counterparts on television advertising in the campaigns for the White House and control of the Senate.

That's eating into President Barack Obama's financial advantage over Mitt Romney and prompting expressions of alarm from top Democrats.

The disparity is most evident in the race for the White House.

Crossroads GPS, Restore Our Future and other organizations aligned with the Republicans spent nearly $37 million on TV ads through the first few days of June, most of it attacking Obama. That compares with about $11 million by groups supporting the president.

Senate campaigns have been affected, notably in Ohio, where Democratic Sen. Sherrod Brown's commanding lead in the polls began to erode after the U.S. Chamber of Commerce and others started a televised attack.