(Adds explanation of why Senate did not confirm Dawn Stump along with other nominees, Giancarlo comment)
WASHINGTON, Aug 3 (Reuters) - The U.S. Senate voted on Thursday to confirm two Republicans and one Democrat to serve on the Commodity Futures Trading Commission, the top U.S derivatives regulator.
In a voice vote, the Senate approved the nominations of Republican Chris Giancarlo to serve as CFTC chairman, as well as Republican Brian Quintenz and Democrat Rostin "Russ" Behnam to serve as commissioners.
However, the Senate did not vote to confirm another Republican nominee, Dawn Stump.
A Senate Democratic aide, speaking on condition of anonymity, said Stump was not on the slate of nominees because the party did not want to approve a total of three Republican commissioners and only one Democrat.
That would leave the CFTC with just one Democratic commissioner because the other one, Sharon Bowen, announced recently that she planned to step down soon.
The aide added that once Republican President Donald Trump selects a second Democrat to replace Bowen, then that person's nomination will likely be approved along with Stump's.
Giancarlo has already been serving as acting CFTC chairman since Trump took office in January.
In a statement, Giancarlo said he was "humbled" by the bipartisan support for him in the Senate. (Reporting by Sarah N. Lynch; Editing by Jeffrey Benkoe and Jonathan Oatis)