Congress and President Bush head into a showdown over the war in Iraq on Thursday after the Senate voted to approve a $124 billion war-funding bill that orders most U.S. troops home within one year. The measure passed on a 51-to-46 vote.
The House voted 218-208 on Wednesday to approve the same bill.
President Bush has vowed to veto the legislation, and congressional Democrats don't have the votes to override a veto.
The current tug of war between Congress and the president may be contentious, partisan and, at times, mean-spirited, but it is far from unprecedented.
"Every time the nation has been at war, there has absolutely been a tussle between the president and Congress," says Ellen Fitzpatrick, a professor of history at the University of New Hampshire.
That friction, she says, is by design. Wary of an all-powerful monarch, the Founding Fathers divided authority, giving the president the right, as commander in chief, to conduct a war and Congress the authority to declare, fund and — to a certain extent — oversee it.
President Bush's accusation that Congress is trying to "micromanage" the war is, historically speaking, nothing new. Presidents from James Madison to Abraham Lincoln to Harry Truman have complained that Congress was hamstringing their ability to fulfill their role as commander in chief — and members of Congress have, just as vociferously, accused presidents of overstepping their authority.
Over the years, power has seesawed. Congress had the upper hand in the 19th century, but since World War II, the power of the presidency has grown, historians say.
"Each successive president used a predecessor to claim precedent," Fitzpatrick says. "[Woodrow] Wilson pointed to Lincoln; FDR pointed to Wilson, and so on."
The pivotal moment, though — the point where power swung decisively from Congress to the presidency — was in 1950. That's when President Harry Truman sent thousands of U.S. troops to Korea under a United Nations mandate. It marked the first time a president dispatched troops into battle without first seeking a congressional declaration of war.
"For Truman, it was a quicker and less politically messy way to send the troops overseas," says Julian Zelizer, a professor of history at Boston University. Ever since, presidents have followed Truman's lead and sent U.S. troops into battle without first asking Congress to declare war.
Recent presidents have argued that in an era of nuclear weapons (and now terrorism), they need to act quickly and don't have time for a protracted congressional debate. In recent decades, Congress has been reluctant to be seen as second-guessing the commander in chief. Even during the Vietnam era, with public opposition to the war growing, Congress moved cautiously.
Zelizer says that should come as no surprise.
"Congress is an incremental institution that revolves around compromise and negotiations — issues where the population itself is not on the same page — so it tends to move slowly. And that is what happened in Vietnam," Zelizer says.
Once Congress does decide to get involved in matters of war, it can wield great power. It can, for instance, specify the geographic extent of a war. That's what it did in the 1970s by ordering U.S. troops out of Cambodia. It can specify the kind of war to be waged, authorizing, for example, an air war and not a ground war, as it did in Kosovo.
Can Congress go further and specify how many troops are deployed to the battlefield and the tactics they use? Most (though not all) constitutional scholars say the answer is no. Those decisions clearly fall to the commander in chief.
Some have called the current debate a question of "funding the troops." That is not exactly true. Congress has withheld funds to wage a war — as it did in 1973 at the tail end of the Vietnam War — but it has never left troops in the field without the resources they need. The current debate is less about funding the troops than about possibly withdrawing them.
In any event, Congress is flexing its muscle over the Iraq war more quickly than it did during Vietnam. That, says Fitzpatrick, is because public opposition to this war is "more unified" than during the Vietnam era.
According to a recent Associated Press poll, 64 percent of those surveyed said they disapproved of President Bush's handling of the war in Iraq.
Whether Congress has misread public sentiment and overplayed its hand is unclear. Nor is it clear what congressional Democrats' next move might be, should the president, as expected, veto any legislation calling for a timetable for troop withdrawal. Some analysts predict they will redraft legislation more acceptable to the White House.
If history is any guide, though, both branches of government are digging in for a long and combative debate over if, and when, to pull U.S. troops out of Iraq.