He's not running in '08, but history shows his bad ratings can swamp the GOP.

AMID ALL THE frenetic early maneuvering in the 2008 GOP presidential race, Republicans may be missing the elephant in the room: namely that the head of the herd is bleeding to death on the carpet.

That would be President Bush, whose approval rating scraped new lows last week. Bush won't be on the ballot in 2008, of course, but throughout American history, outgoing presidents have cast a long shadow over the campaign to succeed them. And when a departing president has been as unpopular as Bush is now, his party has usually lost the White House in the next election.

There's no guarantee that history will repeat itself. But the weight of experience suggests that Republicans in Congress and in the presidential race are vastly underestimating the challenge of escaping the undertow Bush is creating. If he cannot recover at least somewhat, or if the party does not separate itself from him more effectively — or both — the GOP may be dragged under.

In the elections to replace departing presidents, weakness seems more contagious than strength. Outgoing presidents with a high job approval rating haven't always succeeded in passing on the White House to their chosen candidates. Ronald Reagan did in 1988, but, in two nail-biting contests, Dwight Eisenhower in 1960 and Bill Clinton in 2000 could not.

Unpopular departing presidents, though, have consistently undercut their party in the next election. Democrats lost the White House in 1952 and 1968 after Harry Truman and Lyndon Johnson saw their approval ratings plummet below 50%. Likewise, in the era before polling, the opposition party won the White House when deeply embattled presidents left office after the elections of 1920 (Woodrow Wilson), 1896 (Grover Cleveland), 1860 (James Buchanan) and 1852 (Millard Fillmore). The White House also changed partisan control when weakened presidents stepped down in 1844 and 1884. Only in 1856 and 1876 did this pattern bend, when the parties of troubled presidents Franklin Pierce and Ulysses S. Grant held the White House upon their departure.

This shouldn't be shocking. Voters dissatisfied with a departing president typically want change. And they usually believe the opposition party will deliver more change than the president's. The most recent elections to replace retiring two-term presidents — Reagan in 1988 and Clinton in 2000 — help us quantify that instinct. In each case, media exit polls found that the same share — 88% — of voters who disapproved of the retiring president's job performance voted against his party's nominee, George H. W. Bush in 1988 and Al Gore in 2000. By contrast, about four-fifths of voters who approved of the outgoing president's performance voted for his party's nominee each time.

Those are ominous numbers for Republicans today. On the day of the election to succeed them, both Reagan and Clinton enjoyed approval ratings just over 55%, with about 40% of voters disapproving. In last week's Gallup/USA Today poll, Bush's approval rating stood at just 29%, with 66% disapproving. If voters divide as they did in 1988 and 2000, and Bush's ratings do not improve, that would translate into a 2008 Democratic landslide. That's why Emory University political scientist Alan Abramowitz says flatly, "There is no way any Republican can win the presidential election next year if Bush's approval rating remains anywhere near where it is now."

In fact, to survive 2008, Republicans will probably need some combination of separation (from Bush) and rehabilitation (for him). But neither end of that equation will be easy. Bush's disapproval rating has exceeded 58% all year and has not fallen below 50% for two years — the longest stretch of such presidential weakness since Truman finished his second term beleaguered by Korea, corruption and Joe McCarthy.

It's true that Republicans in 2008 should perform slightly better among voters who disapprove of the president than George H.W. Bush and Gore did, because their nominee, unlike those men, won't be the retiring president's vice president. But another pattern underscores how hard the challenge will remain: On average, 80% of voters who disapproved of a president's performance have voted against his party's candidates even in House races since 1986, according to the respected University of Michigan post-election polls. When a president takes on water, in other words, everyone in his party flounders.

One senior GOP strategist says Bush could most help the party by redirecting the American mission in Iraq away from front-line combat operations toward training and counter-terrorism. But even if Bush dropped his opposition to that idea, such a change might be too little, too late to rebuild his public standing. Whatever Bush does in Iraq, Republicans next year will probably need to paddle away from him much more energetically than they have so far. It also means that no matter how hard they swim, they could still be swamped if Bush can't stabilize his sinking ship.