Could it be possible that after George H. W. Bush, the 41st President of the United States, fell from a 90 percent approval rating in 1991 to defeat by Bill Clinton in 1992, that much the same thing might happen to his son?

Could George W. Bush, the 43d President, now standing high as the able leader of the "war on terrorism," be toppled into defeat in 2004?

First of all, in any attempt to answer that question, one has to deal with the oldest, most intractable rule of politics: you can't beat a horse with no horse.

So no matter what else happens in the next year or so, if Bush Jr. is to be beaten in 2004, the Democrats have to come up with a horse ? someone with sufficient national standing to defeat an incumbent President. Or else, and far less likely, that President has to be thrown out by an insurgent from his own party.

Even if either of those scenarios were to unfold, however, a campaign against George W. Bush probably would be fruitless if he were able to run for re-election approximately as he is today ? a popular chief executive who has led a popular war in an impressive manner that led to a quick and nearly bloodless victory over a despised opponent ? and also a good measure of revenge for Sept. 11.

That's where something like the shadow of a doubt arises ? because three years from now, in 2004, Bush almost certainly will not be as he is today, owing to the second oldest law of politics: anything can happen before the election, especially if it's a long way off. Ask No. 41, George H. W. Bush, about that second law.

He found, for one thing, that the victorious Gulf War against Iraq was a lot easier to get into, and even win, than to get out of. To have thrown out Saddam Hussein would have left the U.S. without a suitable replacement government and with a host of new problems as an occupying Western nation amid a sea of surrounding Arab states.

The problem of No. 43, George W. Bush, in finding an exit from the war on terrorism is different but still complex. If, for instance, he parlays the momentum of victory over the Talilban into an attack on Iraq, as many in his party, in Congress and even in his Administration are urging, he will find nothing like the national unanimity and popularity that have supported the war ? and himself --until now.

In that event, also, the fragile international coalition that has so far backed the war on terrorism might come apart ? notably in Pakistan but in other Muslim countries as well ? with significant domestic political reverberations.

If, on the other hand, Bush does not move on to an attack on Iraq, leaving Saddam Hussein once more in power in Baghdad, a substantial portion of the public, Congress and his own Administration will believe ? as many feel about No. 41 ? that he failed to complete the job.

Either way he moves on Irag, therefore, could be damaging politically at home. Or suppose he does not officially either attack or refuse to attack ? in effect, choosing a middle way, leaving Hussein under threat of war and overthrow but Iraq not actually being bombed or attacked. In the latter event, the war on terrorism might seem to be petering out ? perhaps with Osama bin Laden yet uncaptured, and the U. S. in its uncomfortably heightened state of alert and alarm.

Meanwhile, a slow but steady undertone of domestic criticism can be heard ? not only about the controversial order for military tribunals of certain captured terrorists, but on the general theme that, under cover of the war emergency, Bush is stealthily imposing some of his pre-Sept. 11 agenda ? particularly environmental -- on a country too emotionally involved in the war on terrorism to object, or even to notice.

Any President, acting as commander-in-chief of the armed forces in wartime, is virtually immune to open criticism. George W. Bush, at the moment, may be entitled to take limited advantage of this shield. But if he moves too strongly ? on drilling in the Arctic refuge, for instance -- or after the emergency has waned, the critics and the opposition will come into the open.

It's true, as Bush has repeatedly warned, that the war against terrorism will be long and difficult. But sooner or later, the nation will return to something like conventional politics. When that reversal occurs, what will the voters see in the White House? The restrained, judicious, more or less non-ideological leader who unified a shocked country for victory against an amorphous but real enemy?

Or the neo-right winger of pre-Sept. 11 days, the loser of the popular vote in 2000? The friend if not the servant of the oil industry? The myopic but determined tax-cutter?

If the former, or a reasonable facsimile, the election of 2004 may well be over before it begins. But if the latter, No. 41 could tell No. 43 that in politics, it's never over till it's over.