For his part, Bush, who also finds himself under assault for the firing of eight U.S. attorneys, the conduct of the Iraq war and alleged abuses in government surveillance by the FBI, is holding firm. Though he has vetoed only one piece of legislation since taking office, he has vowed to veto 16 bills that have passed either the House or Senate in the three months since Democrats took control of Congress.

Despite the threats, Democratic lawmakers expect to open new fronts against the president when they return from their spring recess, including politically risky efforts to quickly close the prison at Guantanamo Bay, Cuba; reinstate legal rights for terrorism suspects; and rein in what Democrats see as unwarranted encroachments on privacy and civil liberties allowed by the USA Patriot Act.

"I suppose there's always a risk of going too far," said House Majority Leader Steny H. Hoyer (D-Md.), "but the risk of not going is far greater."

Backed by a unified party and fresh from a slew of legislative victories, Democratic leaders appear to believe there is hardly any territory they cannot stray onto, a development that has Republican political operatives gleeful and some Democrats worried. Rep. Tom Cole (Okla.), chairman of the National Republican Congressional Committee, warned of a "political price" at the polls: "If they let their constituents and their ideology drive them past the point where the American people are comfortable, they will find how quickly the voters will react."

Leon E. Panetta, who was a top White House aide when President Bill Clinton pulled himself off the mat through repeated confrontations with Congress, sees the same risk. He urged Democrats to stick to their turf on such issues as immigration, health care and popular social programs, and to prove they can govern.

"That's where their strength is," Panetta said. "If they go into total confrontation mode on these other things, where they just pass bills and the president vetoes them, that's a recipe for losing seats in the next election."

But even conservative Democrats insist their party is in no danger of overreaching its mandate from the November elections. Rep. Baron P. Hill (Ind.), a conservative Democrat who squeaked out a victory in November against the Republican who had taken the seat from him two years earlier, said he was concerned early on that Democratic leaders would mount a "witch hunt" against Bush and his policies. But, he said, they are far from any witch hunts.

The view is decidedly different from the White House. In three months, Democrats have pushed back hard on the Bush legacy. A House-passed bill would require the government to negotiate prices for prescription drugs for Medicare beneficiaries, highlighting what Democrats consider a shortcoming of the president's landmark Medicare prescription drug law. Bush has promised a veto.

A Senate-approved measure would allow screeners at the Transportation Security Administration to unionize, prompting a veto threat. White House opposition to that in 2002 led to a legislative standoff over the creation of the Department of Homeland Security that proved devastating to Democrats, who were painted as soft on terrorism.

A bill to ease the public release of official papers from presidential libraries also yielded a veto promise, although it passed with overwhelming bipartisan support. The measure would reverse one of Bush's own executive orders, which has helped keep reams of presidential documents under lock and key.

Budgets passed by the House and Senate assume the expiration of most of Bush's tax cuts in 2012, and Democrats are demanding tough new standards for labor rights and environmental regulations as a condition of extending the president's authority to expedite trade negotiations.

The White House has also vowed to block two separate House bills that would extend whistle-blower protections to national security and to rail security workers.

But it is the legislation coming down the pike that promises the real fireworks. Most Republicans are convinced the president will win his veto standoff over House and Senate war spending bills that would impose mandatory troop withdrawals from Iraq.

"It's going to be like the government shutdowns" of 1995 and 1996, predicted Rep. Jack Kingston (R-Ga.). "The Democrats' honeymoon is fixing to end. It's going to explode like an IED."

That would slow their momentum as they challenge Bush on the territory he has made his political fortune on: terrorism. But Democrats are undaunted in their demands to close the prison at Guantanamo Bay. They also want to reopen last year's law creating military commissions to restore the right of habeas corpus to terrorism suspects and to revise rules that allow convictions to be based in part on evidence yielded by interrogation methods that critics call torture.

"We have a very consequential and just system of justice. To create a system that is a dual system but not just is not acceptable, and that's Guantanamo," said Sen. Dianne Feinstein (D-Calif.). Democratic leadership aides are most skittish about the Patriot Act, saying they would only temper it by eliminating a provision that allows the indefinite appointment of U.S. attorneys without Senate confirmation and by tightening the FBI's use of "national security letters" to obtain private information about U.S. citizens.

For Republicans, such legislative gambits could prove to be a political gift. When reports first surfaced of plans to close Guantanamo Bay and send terrorism suspects to military prisons in the United States, Republicans accused Democrats of planning to import terrorists to U.S. soil. Even after Defense Secretary Robert M. Gates suggested he could support the idea, Rep. Duncan Hunter (R-Calif.) pressed the attack Friday.

"The idea that we would import dangerous terrorists, like Khalid Sheik Mohammed, into American communities is dangerous," Hunter said at a hearing of the House Armed Services Committee, of which he is the ranking GOP member.

Sen. Lindsey O. Graham (R-S.C.) has already raised the specter of justice grinding to a halt as terrorists use their access to federal courts under the right of habeas corpus to blitz the judicial system with lawsuits.