"Josh Mandel's always willing to highlight his fundraising numbers," said Ohio Democratic Party spokesman Justin Barasky. "But Ohioans want to know why he refuses to stand up for Ohio jobs and workers by taking a position on China's unfair currency manipulation, why he won't fight against job killing trade agreements, and why he continues to break the law by not disclosing his personal finances." 

A first-term senator facing a difficult reelection, Brown has amassed almost $4.2 million in the bank, thanks in part to out-of-state donors who made up about 40 percent of Brown's third-quarter haul.

Mandel has not released his cash on hand figure or other fundraising details, but that information will be released when the two candidates file their official reports by Oct. 15.

Mandel, the Ohio state treasurer, is a relatively new face on the political scene, but is leading the contest for the Republican nomination to challenge Brown.

"We are in a unique position where we don’t have a competitive primary and all Republican factions are coalescing behind our candidacy," said Mandel spokesman Joe Aquilino.

Although President Obama's numbers are underwater in Ohio — 53 percent disapprove of his performance — Brown has managed to maintain a substantial lead over his presumed Republican opponent. He led Mandel by 13 points in a Quinnipiac University poll of Ohio voters released Sept. 28.