I think the POTUS approval poll is overrated for this purpose (except to push a twisted sort of bandwagon effect).
I didn't vote for Trump to be my Congressional Representative in either the House or the Senate. He wasn't running for that job. He wasn't running for Governor of my State, nor any of those other offices that work to make things happen at the State or local level.
I think that the Democrats are underestimating the actual focus on the candidates for Congress, especially in districts where it is obvious that incumbents just haven't been listening to the people and have been marching in lockstep with people who want to fund fraud, go soft on crime, open the borders, and who basically embrace policies that led to the actual mechanics of Bidenomics and the theft of (hundreds of?) Billions of dollars from the public coffers through fraud, NGOs, and a host of other cut-outs that amounted to money laundering and wholesale corruption. That includes the response to COVID as well.
Trump may be the de facto face of the Republican party by virtue of being POTUS, but the people running for Representative, Senator, Governor, and a host of other offices are the ones who either haven't been doing their jobs, have done them at least passably well (and better than other potential alternatives), or are trying to get a shot at truly representing their possible future constituents (at least until 'Beltway Fever' sets in).
What Trump does really has little direct effect on the way your representatives will represent you, your fraction of America and its needs and wants--which may vary greatly from the overall National Agenda set by any POTUS. You aren't hiring them for Trump (or against him), you are hiring them for you, to represent you, and let the chips fall where they may.