The resignation of perhaps the Republican National Committee's No. 1 fundraiser sent another signal Monday of ongoing turmoil within the organization.

Sam Fox, a U.S. ambassador to Belgium under former President George W. Bush, has left his post, according to a report by Politico's Ben Smith.

Another top GOP fundraiser told Smith that Fox had "lost confidence" in RNC Chairman Michael Steele, and was "deeply troubled by the pattern of self-inflicted wounds and missteps" at the RNC.

Fox was working pro bono for the RNC as co-chairman of the Republican Regents, its top fundraising board.

Fox was "one of the RNC's few remaining connections to the deep-pocketed Republican establishment and was viewed as the heaviest hitter among its fundraisers," Smith wrote.