President Bush has kept his promise to veto legislation that tied funding for military operations in Iraq to a timeline for U.S. troops to leave the country.
Bush accused Democrats of using the funding bill to foster a political point.
But Democratic leaders countered that the legislation, which ties $124 billion to pulling out troops starting in October — represented the will of the American people who want an end to an unpopular war.
The veto Tuesday evening was only the second time that Bush used such power. The first rejected federal funding for stem-cell research.
"I asked the Congress to pass an emergency war-spending bill that would provide our brave men and women in uniform with the funds and flexibility they need," he said. "Instead, members of the House and the Senate passed a bill that substitutes the opinions of politicians for the judgment of our military commanders."
In a symbolic gesture, the president issued the veto using a pen that was given to him by the father of Marine Reserve Cpl. Dustin Derga of Columbus, Ohio. Derga was killed in fighting in Iraq's Anbar province two years ago this month.
Bush called the troop withdrawal deadline rigid and unacceptable as it would have required the pullout to begin no later than October 1, with a non-binding goal of all combat troops out of Iraq by March 31.
"It makes no sense to tell the enemy when you plan to start withdrawing. All the terrorists would have to do is mark their calendars and gather their strength, and begin plotting how to overthrow the government and take control of the country of Iraq," he said.
Calling a deadline for withdrawal is the same as setting a date for failure Bush said his new strategy, including increasing the size of the U.S. force in Iraq, needs time to work. He warned that if funding isn't approved soon the military will begin to face shortfalls.
But there was symbolism for the Democrats as well. They sent the funding bill to the president on the fourth anniversary of his declaring an end to combat operations in Iraq while standing in front of a banner that read "Mission Accomplished."
For his critics it's a moment that underscores how wrong the President has been about the war from the beginning.
Democrats insisted that the bill they sent to the White House reflected what the American people want.
"The president may be content with keeping our troops mired in the middle of an open-ended civil war, but we're not, and neither are most Americans," Senate Majority Leader Harry Reid said.
House Speaker Nancy Pelosi said the legislation contained the money the troops and the mission need, and that it's Bush who's stalling the process.
"The president wants a blank check. The Congress is not going to give it to him," Pelosi said.