Four G.O.P. senators crossed party lines to back the resolution to direct President Trump to halt the war in Iran and seek authorization from Congress, but their support was not enough.
The vote on Tuesday reflected a determination among Democrats to continue aggressively pushing back on President Trump’s handling of the war with Iran.
Democrats demanded an immediate briefing and even Republicans conceded they had no information on an agreement the administration has declined to release.
Senator John Thune of South Dakota, the majority leader, said that he had not yet seen the deal but said he expected the administration to convene with lawmakers as the process continues.