They plan to go through with their agenda, giving no thought to the consequences of their actions. Bush has promised to veto 16 pieces of legislature and if he goes through with it, then what will the Democrats have? Nothing. They’ll have nothing to show for their effort. They can go back to their constituents and say that it was Bush’s fault, he vetoed it but their opponent in 2008 has a very case against them. They could have compromised and worked with the president to overcome his veto threat but they choose to fight instead of legislate.

Even as their confrontation with President Bush over Iraq escalates, emboldened congressional Democrats are challenging the White House on a range of issues — such as unionization of airport security workers and the loosening of presidential secrecy orders — with even more dramatic showdowns coming soon.
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 the 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.”

They passed that point when they went on vacation and left our troops underfunded. They have a constitutional obligation to fund the troops during a time of war that they are shirking.
If they weaken our security by their actions, they own the consequences of any future hits. I really don’t see them wanting to own this war at all.
BTW, I find Obama’s statement fascinating in light of this new toughness:

If President Bush vetoes an Iraq war spending bill as promised, Congress quickly will provide the money without the withdrawal timeline the White House objects to because no lawmaker “wants to play chicken with our troops,” Sen. Barack Obama said Sunday.
“My expectation is that we will continue to try to ratchet up the pressure on the president to change course,” the Democratic presidential candidate said in an interview with The Associated Press. “I don’t think that we will see a majority of the Senate vote to cut off funding at this stage.”
[…]
Given that Bush is determined to veto a timetable for withdrawing U.S. troops from Iraq, Congress has little realistic choice but to approve money for the war, Obama said.
“I think that nobody wants to play chicken with our troops on the ground,” said Obama. “I do think a majority of the Senate has now expressed the belief that we need to change course in Iraq.
“Obviously we’re constrained by the fact that a commander in chief who also has veto power has the option of ignoring that position,” Obama said.

(via)
Yes, that’s right Bush does have the power to veto, good of you to remember that. You might want to mention that to Pelosi.
And your majority was razor thin, wasn’t it?
Obama is wrong that “nobody wants to play chicken with our troops on the ground,” Kos does. Go check out his reaction to Obama’s statement at Little Green Footballs, it’s pretty funny (well, it would be if we weren’t dealing with a serious issue here).