Since Bush is still hugely popular in many areas of the country, I’d say that most Republicans will want him when they campaign in Montana or Idaho or rural Michigan or Indiana. on the other hand, I’m sure whoever is running against Charlie Rangel in NYC will avoid a Bush appearance.
For the people who those candidates want to motivate to get out the vote - strongly conservative Republicans - the President is still very popular, and he’ll still be a welcome draw at campaign events into the foreseeable future.
That said, the handful of moderate Republican members of Congress and senators have always regarded a Bush campaign stop as a mixed blessing, and will probably be even a bit more reluctant to see Air Force One fly into their districts/states, given recent polling.
The problem, of course, as always, is that this is about people’s opinions on Congress as a whole, not about their respective senators or representatives. Opinions of Congress as a whole are always poor, but it’s always due to “the other guys; my guy is fine.” So 90% of these fuckers will get re-elected, at minimum, regardless of how crappy a job, in general, people think they’re doing. It’s a permanent paradox that won’t change any time soon.