Clinton and Eisenhower would be slam dunks. Reagan is iffy due to his age. Bush would be DOA.
Not so much. Eisenhower was pretty old too - if memory serves approaching 70. He'd also had 2 heart attacks. We also can't assume all these people would've had second terms identical to IOTL; they might've governed a bit differently if they were running for re-election, and the opposition party's candidates might've been completely different as well
Conversely, Bush's second term might be much different - no surge, stricter regulations on fanny and Freddy, etc might've helped keep his approvals over 40%. He'd fight a very difficult battle, but all in all I wouldn't completely discount it if the financial crisis is kept at bay and the Dems nominate someone very lackluster. (Kerry v. Bush or Bush v. Gore rematch anyone
)
Finally, with Clinton, I don't understand why everyone thinks a third term would be a slam dunk. Lewinsky would've hit him harder, and W campaigning as a family values crusader would've been pretty appealing to people disgusted with Slick Willy's conduct. Maybe the GOP realizes the best strategy is to allow people to be outraged but not politicize it too much by impeaching him = no "poor me" effect. Finally, Bill had some health problems of his own - the otl stress of Lewinsky, governing the country for 8 years, etc, and add to that the task of what would likely be a very close re-election bid, it's possible he makes it out 3 terms alive, but things don't look too good. A fourth term bid might kill him.