Approval rating is different from preference, which is what the OP was talking about. He may have only a 40% approval rating, but if the approval rating of a pu

Approval rating is different from preference, which is what the OP was talking about. He may have only a 40% approval rating, but if the approval rating of a putative Democratic opponent is lower, he'd still win an election. Of course he (supposedly) can't be on the ballot any more, but a midterm election is always seen as a referendum on the President. If Democrats win in November they have some ability to hamper his ability to do... whatever it is people voted for him to do. A 40% approval rating for the President doesn't bode especially well for him in November. But "Democrats in Congress" have an 18% approval rating, so voters aren't thrilled with them, either.