A Marine veteran and former state lawmaker elected state treasurer in 2010, Mandel is facing scrutiny over contributions he and Rep. Jim Renacci (R-Ohio) accepted from almost two dozen employees of a direct-marketing firm.

Mandel announced Wednesday that he was returning $105,000 in donations out of an abundance of caution while the FBI investigates the contributions, the Cleveland Plain Dealer reported. Renacci is taking a wait-and-see approach.

Mandel and Renacci have maintained that the donors, not the campaigns, are the subjects of federal inquiry. Brown’s campaign said Mandel had been shamed into returning the money and called it further evidence that he can’t be trusted.

The poll of 1,103 Ohio voters was conducted May 17-20 and had a margin of error of plus or minus 3 percentage points.