There's something about contemporary American politics where it almost always helps to be on defense. There's not much of an incumbency bonus anymore; rather, it often helps to be the opposition, the out-party, the "underdog", if you will.
The president (both presidents in general and Trump in particular) rarely plays defense. But he has been able to do in both a literal and figurative sense in the House's impeahment process. And indeed, there seems to have been at least some uptick in Trump's approval rating.
But in the Senate, it's more equivocal, with Roberts presiding, McConnell setting rules, the presumed verdict being no conviction, probably a high propensity from GOP managers to sound partisan, etc. Trump will be on defense in a literal sense but maybe *not* in a figurative one.
