Washington ? The Senate on Monday refused for a second time to confirm John Bolton as U.S. ambassador to the United Nations, prompting his supporters to urge President Bush to bypass Congress and give the controversial nominee a recess appointment, which would last 18 months.

The vote was a setback for Bush, whose party controls the Senate, and the latest in a string of partisan impasses that also have stymied his efforts to appoint judges and restructure Social Security. Some senators said a recess appointment now appears to be Bolton’s only hope even though it would be politically contentious and would send him to the United Nations under a cloud. That action could come as early as July 2.

Republicans denounced Democrats as obstructionists after Monday’s vote. But Democrats said Bush deserves the blame for tapping a nominee known for his combative style and criticism of the United Nations and then rejecting lawmakers’ requests for documents related to his tenure at the State Department.

The Senate voted 54 to 38 to end debate on Bolton’s nomination. That was six votes short of the 60 needed to stop filibusters in the 100-member chamber.

Several senators said Bolton could have won a simple confirmation vote if the filibuster had been ended. But with no sign of a compromise between Democrats and the White House over the disputed documents, several lawmakers said they saw no strategy that would pick up the half-dozen votes needed to end debate and allow a confirmation vote.