And what would such payment stops do to the economy? Nothing good. Consumer spending would probably crash, as nervous seniors started wondering how to pay for rent and food. Businesses that depend on government purchases would slash payrolls and cancel investments.

Furthermore, markets might well panic, especially if interest payments are missed. And the consequences of undermining faith in U.S. debt might be especially severe because that debt plays a crucial role in many financial transactions.

So hitting the debt ceiling would be a very bad thing. Unfortunately, it may be unavoidable.

Why? Because this is a hostage situation. If the president and his allies operate on the principle that failure to raise the debt ceiling is an unthinkable outcome, to be avoided at all cost, then they have ceded all power to those willing to bring that outcome about. In effect, they will have ripped up the Constitution and given control over America’s government to a party that only controls one house of Congress, but claims to be willing to bring down the economy unless it gets what it wants.

Now, there are good reasons to believe that the G.O.P. isn’t nearly as willing to burn the house down as it claims. Business interests have made it clear that they’re horrified at the prospect of hitting the debt ceiling. Even the virulently anti-Obama U.S. Chamber of Commerce has urged Congress to raise the ceiling “as expeditiously as possible.” And a confrontation over spending would only highlight the fact that Republicans won big last year largely by promising to protect Medicare, then promptly voted to dismantle the program.

But the president can’t call the extortionists’ bluff unless he’s willing to confront them, and accept the associated risks.

According to Harry Reid, the Senate majority leader, Mr. Obama has told Democrats not to draw any “line in the sand” in debt negotiations. Well, count me among those who find this strategy completely baffling. At some point — and sooner rather than later — the president has to draw a line. Otherwise, he might as well move out of the White House, and hand the keys over to the Tea Party.