Spurred by President Bush's slumping approval ratings, the Republican-controlled Senate - for the first time - is drawing lines in the sand over war, pushing the White House on issues ranging from treatment of detainees to strategy in Iraq.
Last month, senators broke with the White House by voting to ban torture. Last week, they demanded accountability on secret overseas detention centers. This week, 76 senators voted to require the White House to deliver quarterly, unclassified reports on progress of the war in Iraq.
Democrats called Tuesday's resolution a symbolic vote of "no confidence" in Mr. Bush. Republicans deny a big rift with his administration and point out that they consulted with National Security Council staff in advance of the vote. But both sides acknowledge a tipping point in relations between Capitol Hill and the executive branch. "It's a big day for Congress - the institution is rearing up and asserting itself," says Sen. Lindsey Graham (R) of South Carolina.
In Japan, Bush said the resolution was "consistent with our strategy," and he called the rejection of the Democratic version a positive step.
It's normal for Congress to cede authority to the White House in times of war. But analysts say that the high visibility of the Iraq war and this president's rapid drop in the polls have forced a re- adjustment faster than in the nation's previous wars.
"This period recalls the early 1970s between Congress and Nixon and the war in Vietnam. The president pushed presidential war powers as far as he could take it, and Congress is now trying to reassert its power in this war," says Julian Zelizer, a professor of US political history at Boston University.
"Not only are Democrats more open to curbing the president's war, but more Republicans no longer see their fate as tied up with the president," he adds.
In a recent CNN poll, fewer than 1 in 10 Americans said they would be inclined to support a Republican who agrees with Bush "on almost every major issue." One in three said they would be most likely to support a Republican who has had both agreements and disagreements with Bush.
In a weekend Gallup poll, a majority of Americans called for withdrawing all troops from Iraq, either immediately (19 percent), or within a year (33 percent)..
Had Senate Republicans wanted to appear in lock step with the White House on the war, they had the votes to simply defeat a Democratic resolution calling for a timetable for withdrawal from Iraq. Instead, they tweaked the Democratic version in a bid for bipartisan support.
"A big, bipartisan vote sends a message to the Iraqis and the White House. It's very, very significant," says Stephen Hess, a public policy professor at George Washington University.
Both resolutions called for calendar year 2006 to be "a period of significant transition to full Iraqi sovereignty ... thereby creating the conditions for the phased redeployment of United States forces from Iraq." They also require the president to report to Congress every three months on issues ranging from the current military mission to "whether the Iraqis have made the compromises necessary for a broad-based and sustainable political settlement."
Denying any rift with the White House on past conduct of the war, Sen. John Warner (R) of Virginia, chairman of the Armed Services Committee, said, "This is a forward looking amendment."
While Pentagon and White House officials say they are constantly reporting to Capitol Hill, this is the first time that lawmakers have specified terms and a timetable for such reports, including the call that they be unclassified.
Another amendment, sponsored by Senator Graham, clarifies the legal rights of detainees. This, along with a provision barring torture, which the White House has threatened to veto, must now be negotiated with the House.
"We are not going to simply allow the administration to do what it wants on detainees, because it is not consistent with our values," says Sen. Carl Levin of Michigan, the ranking Democrat on the Senate Armed Services Committee.