US President George W. Bush on Tuesday night vetoed legislation to pull US troops out of Iraq in a historic showdown with Congress over whether the unpopular and costly war should end or escalate. It was a day of high political drama, falling on the fourth anniversary of Bush's "Mission Accomplished" speech declaring that major combat operations had ended in Iraq. In only the second veto of his presidency, Bush rejected legislation pushed by Democratic leaders that would require the first US combat troops to be withdrawn by Oct. 1 with a goal of a complete pullout six months later. "This is a prescription for chaos and confusion and we must not impose it on our troops," Bush said in a nationally broadcast statement from the White House. He said the bill would "mandate a rigid and artificial deadline" for troop pullouts, and "it makes no sense to tell the enemy when you plan to start withdrawing." Democrats accused Bush of ignoring Americans' desire to stop the war, which has claimed the lives of more than 3,350 members of the military. "The president wants a blank check," said House Speaker Nancy Pelosi, moments after Bush's appearance. "The Congress is not going to give it to him." She said lawmakers would work with him to find common ground but added that there was "great distance" between them on Iraq. The legislation amounted to a rare rebuke of a wartime president and an assertion by Democrats that Congress must play a major role in Iraq and the extent of US involvement. Senate Majority Leader Harry Reid said Bush has an obligation to explain his plan for responsibly ending the war. "If the president thinks by vetoing this bill, he'll stop us from working to change the direction of the war in Iraq, he is mistaken," Reid said. Lacking the votes to override the president, Democrats have already signaled they intend to approve a replacement bill stripped of the troop withdrawal timetable. Determined to challenge Bush's policy, they are turning their attention to setting goals for the Iraqi government to meet as it struggles to establish a more secure, democratic society. The White House and congressional Republicans have also called for so-called benchmarks, but only if they don't mandate a troop withdrawal or some other major change in war policy. Bush will meet with congressional leaders, Democrats and Republicans alike, on Wednesday to discuss new legislation. He said Democrats had made a political statement by passing anti-war legislation. "They've sent their message, and now it's time to put politics behind us and support our troops with the funds," the president said. He said the need to act was urgent because without a war-funding bill, the armed forces will have to consider cutting back on buying or repairing equipment. "Our troops and their families deserve better, and their elected leaders can do better," Bush said. "Whatever our differences, surely we can agree that our troops are worthy of this funding and that we have a responsibility to get it to them without further delay," the president said. Minutes after Bush vetoed the bill, an anti-war demonstrator stood outside the White House with a bullhorn: "How many more must die? How many more must die?" Earlier at the Capitol, Democrats held an unusual signing ceremony of the $124.2 billion bill before sending it to the White House. "The president has put our troops in the middle of a civil war," said Reid. "Reality on the ground proves what we all know: A change of course is needed." For his part, Bush flew to Florida to meet with military commanders and said the Democratic proposal would turn Iraq into a "cauldron of chaos." With sleeves rolled up, Bush shook hands with troops at MacDill Air Force Base in Tampa, the headquarters of US Central Command, which oversees military operations in the Middle East, including Iraq. Then Bush returned to the White House to announce his veto just before network news shows. Democratic leaders refused to discuss their approach to Wednesday's meeting with Bush. Past meetings have not led to any compromises, although members said this time they hoped Bush would signal a willingness to negotiate. "I don't want to get into a negotiation with myself," Reid said when asked about conversations with Senate Republican leader Mitch McConnell. McConnell and other Republicans have said they would agree to provisions that lay out standards for the Iraqi government to meet in creating a more stable and democratic society. "A number of Republicans think that some kind of benchmarks properly crafted would be helpful," McConnell said. Bush and his Congressional allies have said they will oppose legislation that ties progress on such standards to a withdrawal of US combat forces. "House Republicans will oppose any bill that includes provisions that undermine our troops and their mission, whether it's benchmarks for failure, arbitrary readiness standards or a timetable for American surrender," said Minority Leader John Boehner. Some Republicans say they would support tying goals for Iraqi self-defense and democracy to the more than $5 billion provided to Iraq in foreign aid. But such an idea has not piqued the interest of Democrats. When Bush announced a US troop increase in January, he said Iraq's government must crack down on both Shiites and Sunnis, equitably distribute oil wealth, refine its constitution and expand democratic participation. He attached no consequences if these benchmarks were not met. Tuesday's developments came exactly four years after Bush's speech on the aircraft carrier USS Abraham Lincoln decorated with a huge "Mission Accomplished" banner. At the time, Bush's approval rating was 63 percent, with the public's disapproval at 34 percent. Four years later, only 35 percent of the public approves of the job the president is doing, while 62 percent disapprove, according to an April 2-4 poll from AP-Ipsos. Bush has used his veto power only once before, when he rejected a measure last summer to lift restrictions on federal money for embryonic stem cell research.