Here's a scenario: Bush is re-elected. Iraq slowly progresses economically and politically. Other rogue nations (Syria, Iran, N. Korea) are tamed by military action or the fear of it. The economic recovery looks like a replay of the 1990s (if not better). Deficits are no longer an issue because tax revenues rise with the recovery. Social Security reform is underway, and there are good prospects for Medicare reform.
Upon Bush's re-election, Edwards and Clinton (of the female gender) instantly become the leading contenders to head the Democrat ticket in '08. By '08 they will have spent almost four years exposing their left-wing positions to the country and bashing each other. Out of that wreckage a less compelling nominee might crawl.
Thus, given my scenario, Republicans should be able to hold onto the White House simply by putting up someone -- not named Bush -- whose politics are to the right of the Democrat nominee's.
Hold that thought.
What about Barack Obama? Too young and inexperienced to be a candidate in '08. But if Repubs hold the White House in '08, look for Obama in '12.