WASHINGTON (CNN) -- President Bush withdrew the nomination of businessman Sam Fox for an ambassadorship Wednesday, as Democrats vowed to block the nominee for his financial support of the conservative group that financed the "swift boat" ads against Massachusetts Sen. John Kerry, D-Massachusetts, the 2004 Democratic presidential nominee.

The withdrawal came hours before the Senate Foreign Relations committee was set to vote on his nomination.

In a February 27 committee hearing, Kerry confronted Fox about his support for the group by asking him "might I ask you what your opinion is with respect to the state of American politics as regards the politics of personal destruction?"

"I did it because politically it's necessary if the other side's doing it," Fox responded regarding his donation to "Swift Boat Veterans for Truth."

Sen. Chris Dodd, D-Connecticut, who is seeking his party's presidential nomination, said in an e-mail to supporters Wednesday morning that Fox was not fit to be ambassador because of his involvement with the group.

"U.S. Ambassadors need to be both responsible and credible, and Mr. Fox's support for an organization known to have spread falsehoods illustrates neither," Dodd said.