Invoking a little used rule on Tuesday, Democrats temporarily shut down television cameras in the chamber, cleared galleries of reporters, tourists and other onlookers, forced removal of staff members and recording devices and stopped work on legislation.
"At its core, this is about accountability - congressional accountability and White House accountability," said Senator John Rockefeller of West Virginia, the top Democrat on the Senate Intelligence Committee.
Democrats were pressing that committee to produce a report on whether the Bush administration misused intelligence on Iraq's weapons to justify the March 2003 invasion. No weapons of mass destruction were found.
Democrats said that report was a year overdue and vowed to close more sessions to pressure Republicans to produce it.
"We're serving notice on them at this moment. Be prepared for this motion every day until you face the reality," said Senate Democratic Whip Richard Durbin of Illinois.
Republicans were outraged.
"The United States Senate has been hijacked by the Democratic leadership," Majority Leader Bill Frist of Tennessee said. "Never have I been slapped in the face with such an affront to the leadership of this grand institution."
Dick Cheney aide Lewis Libby
quit after his indictment
Democratic Leader Harry Reid of Nevada said the indictment of Lewis Libby, who was Vice-President Dick Cheney's chief of staff, "provides a window into what this is really about: how the administration manufactured and manipulated intelligence in order to sell the war in Iraq and attempted to destroy those who dared to challenge its actions".
Libby was indicted on Friday on charges of obstructing justice, perjury and lying after an investigation into the public identification of a CIA operative whose diplomat husband was a critic of the Bush administration's case for the war in Iraq.
Senator Christopher Bond, a Missouri Republican on the Intelligence Committee, said the panel was working on the Iraq weapons report and accused Democrats of exploiting Libby's indictment "to say that the war was based on politicised intelligence".