President Bush is sending the National Guard to the Mexican border in hopes of boosting his approval rating. But perhaps it would be more efficient simply to have them arrest the pollsters. Or at least have them eavesdrop on the survey calls and disconnect the disapprovers.

Any day when there is word of a new poll coming out must give White House aides the shakes. It seems that every new survey leads to the headline, “worst of his presidency.” About the only solace for Bush these days is the likelihood that if his approval numbers ever get back into the high 30s, it can be called a comeback.

But there is no escaping the harsh truth that a president stuck under 40 percent approval for a full quarter, as Bush has been since February, is a president who has lost his command. Sure, he retains his formal powers. But given the limited authority that the Constitution specifically grants to the executive branch, the greater source of presidential power is political, not legal.

This poses an opportunity for Congress to reassert its constitutional pre-eminence, but that won’t play out until the November election determines which party will be in control for the final two years of the Bush presidency. Which means that the nation’s capital looks to be the world’s biggest power vacuum for the next several months.

Presidents rule by the intangibles, an almost mystical blend of public relations and political skills that allow them to leverage public support in a way that subdues Congress, the media and all other obstacles in their path. Otherwise they are left with the mostly ministerial duties detailed in the Constitution. Indeed, some of the nation’s founders proposed naming the office “Chief Magistrate,” but eventually they settled on the loftier sounding title in deference to George Washington’s personal popularity.

If pollsters were around in Washington’s day and found job approval figures as low as Bush’s, the initial architecture of the presidency might have been even shakier than it was. Some say the office makes the man, but I submit it is just the reverse. Every president must create and maintain his authority to govern.

And like it or not, the approval rating reported by pollsters has become a prime tool for strengthening — or weakening — a president’s intangible powers. That is why they get the shakes at the White House when the polls come out. With every “unprecedented low” that is reported, Bush loses a bit more wattage, especially in a Congress where many in his own party fear for their own re-elections if they get too close to him.

You know the White House is desperate when they resort to dispatching the first lady to the airwaves to discount the polls and blame the media. Laura Bush — who is the highest-rated figure in the entire administration precisely because she stays above the fray — defended her husband’s dismal numbers in a May 14 appearance on ABC’s “This Week,” saying she doesn’t “really believe those polls” and accusing the media of downplaying her husband’s past strength in public opinion while now having “a lot of fun” with his current decline.

Nice try, Mrs. Bush. Wonder if she believed the polls when he was at 90 percent approval, which got plenty of coverage in the news media, despite her protestations to the contrary. And I can find no signs that mainstream journalists are gleeful about reporting these latest numbers.

The other last gasp of a failing politician that we are likely to hear soon is the inevitable comparison to Harry S Truman, who famously won re-election despite polling predictions that he would lose in 1948. Invoking Truman is always a clear sign that you have run out of arguments.

The question now is, what does a country do with a discredited president? The answer would be obvious if the Constitution provided for a recall election like the one that ousted Gray Davis from the California governor’s mansion nearly three years ago. In the British system, Bush would most likely be forced to call for a new election. Impeachment is one tool legally available, but it is impossible to imagine casting out a president for having low approval ratings.

The congressional results in November could be a way to ratify or reject Bush’s authority to govern, but that could get murky. If Democrats win control of one or both halves of the Capitol, they will certainly interpret their victory as the end of the Bush era. But if Republicans keep control, will it reinvigorate the Bush presidency? Not likely, unless his approval ratings are back up.

Maybe it is a testament to the order and stability of the system that our founders created that when a president is in a fix like the one Bush is in, we are stuck with him until his term runs out. And the dominant power shifts to Congress, which is where the authors of the Constitution meant for it to be all along.

Contributing Editor Craig Crawford is a news analyst for MSNBC, CNBC and “The Early Show” on CBS. He can be reached at ccrawford@cq.com.