The founders would have been astonished by President Bush’s assertion that Congress should simply write him blank checks for war. They gave Congress the power of the purse so it would have leverage to force the president to execute their laws properly. Madison described Congress’s control over spending as “the most complete and effectual weapon with which any constitution can arm the immediate representatives of the people, for obtaining a redress of every grievance, and for carrying into effect every just and salutary measure.”Well, yes, they have those tools. The problem is that those tools, like any weapons in a struggle, need to be credible to be effective. The opposition has to believe that there's a serious possibility that you may use them, or they can behave as if those weapons don't exist. The Executive Branch knows that damned well, because they spent most of the Cold War obsessing over such things: without a credible threat, MAD doesn't work.
The framers expected Congress to keep the president on an especially short leash on military matters. The Constitution authorizes Congress to appropriate money for an army, but prohibits appropriations for longer than two years. Hamilton explained that the limitation prevented Congress from vesting “in the executive department permanent funds for the support of an army, if they were even incautious enough to be willing to repose in it so improper a confidence.”
As opinion turns more decisively against the war, the administration is becoming ever more dismissive of Congress’s role. Last week, Under Secretary of Defense Eric Edelman brusquely turned away Senator Hillary Clinton’s questions about how the Pentagon intended to plan for withdrawal from Iraq. "Premature and public discussion of the withdrawal of U.S. forces from Iraq reinforces enemy propaganda that the United States will abandon its allies in Iraq,” he wrote. Mr. Edelman’s response showed contempt not merely for Congress, but for the system of government the founders carefully created.
The Constitution cannot enforce itself. It is, as the constitutional scholar Edwin Corwin famously observed, an “invitation to struggle” among the branches, but the founders wisely bequeathed to Congress some powerful tools for engaging in the struggle. It is no surprise that the current debate over a deeply unpopular war is arising in the context of a Congressional spending bill. That is precisely what the founders intended.
Does Congress pose a credible threat? Nope. The Administration knows that spending threats are toothless, because the Dems won't do what the Republican threatened to and pull the trigger on the "nuclear option", getting rid of the filibuster. The Republicans know quite well how to make such a threat credible; that's why you had all those senators cross the line to "keep their powder dry", because people believed the Republicans would actually do it. Nobody thinks the Dems have the stones.
As for impeachment, that's an even nastier situation. The Dem leadership said that that's "off the table", despite the threat being a very powerful weapon in the struggle against the President. Yes, he's unlikely to be convicted... and, yes, Cheney would be a worse president. No doubt. But that's the thing: the very act of impeachment would be a powerful symbol of revulsion even were the conviction not to take place, and Bush is at the time of his presidency where symbols mean a whole lot. Sure, Cheney just wants to enrich his buddies and hunt/drive into extinction every cuddly fluffy animal he can get his mitts on, but George is just delusional enough to believe he can go down as anything but the worst non-slavery defending president in American history, and he'll care about that.
But since they're demonstrating that they won't pull the trigger, they might as well not even have the weapon. And if they don't have the weapon, they aren't going to deter Bush, now, are they?