President Bush expressed frustration Wednesday that Iraqis have so far failed to form a unity government, but he said withdrawing U.S. troops from Iraq too early would damage U.S. security.

"I want the Iraqi people to hear I've got great confidence in their capacity to self-govern," Bush said. "I also want the Iraqi people to hear — it's about time you get a unity government going.

"In other words, Americans understand you're newcomers to the political arena. But pretty soon it's time to shut her down and get governing."

The successful creation of a unified central authority remains key to the hoped-for start of an American troop withdrawal this summer. Withdrawing U.S. troops before Iraqi security forces can protect the fragile democracy, however, would yield adverse results, Bush said.

"While it might sound attractive to some, it would have disastrous consequences for American security," Bush said in his third speech this month trying to bolster public support for the war.

If democracy fails, Bush predicted that terrorists would use Iraq as a base to overthrow moderate governments in the Middle East and launch further attacks against the United States.

Bush spoke to Freedom House, an independent organization that supports democracy worldwide, before flying to Cancun, Mexico, to meet with Mexican President Vicente Fox and Canadian Prime Minister Stephen Harper.

Congressional Democrats, meanwhile, proposed a strategy on Wednesday for protecting Americans at home and abroad — an election-year effort aimed at changing public perception that Republicans are stronger on national security.

In the strategy, Democrats vowed to provide U.S. agents with the resources to eliminate Usama bin Laden and ensure a redeployment of U.S. forces from Iraq in 2006. They promised to rebuild the military, eliminate the United States' dependence on foreign oil and implement the recommendations of the Sept. 11 commission.

"The president can give all the speeches he wants, but nothing will change the fact that his Iraq policy is wrong," said Senate Minority Leader Harry Reid, D-Nev.

"Two weeks ago, he told Americans that Iraqis would control their country by the end of the year. Last week, he told us our troops would be there until at least 2009. These mixed messages from President Bush are taking America in the wrong direction and jeopardizing Iraq's chances for success."

Vice President Dick Cheney said the Democrats' behavior has been inconsistent with what they're now promising to do. Cheney said he did not believe the Democrats had a credible plan for tracking down bin Laden and their plan to move U.S. forces out of Iraq this year would amount to a strategic retreat.

"It makes no sense at all to turn Iraq over to the terrorists," Cheney said on FOX News Talk's "The Tony Snow Show."

Jim Manley, a Reid spokesman, responded: "The vice president's tough-talking rhetoric is no longer credible. The Republican game plan to distort and divide will fail because they can't run on their record. All they have are catchy sound bites."

The United States has been pushing Iraq to speed up the formation of a unity government, seen as the best option to subdue the violence gripping several Iraqi cities.

Hundreds of Iraqis have been killed in sectarian violence since the Feb. 22 bombing of an important Shiite shrine in Samarra.

Political talks remain fragile in a country with deep sectarian differences between Shiites and Sunnis. U.S. Ambassador Zalmay Khalilzad has asked one of Iraq's most prominent Shiite politicians to seek the withdrawal of Prime Minister Ibrahim al-Jaafari's contentious nomination for a second term.

Bush countered critics who wonder whether toppling Saddam Hussein caused the current divisions and instability.

"In fact, much of the animosity and violence we now see is the legacy of Saddam Hussein," Bush said. "He is a tyrant who exacerbated sectarian divisions to keep himself in power."