Anything difficult is effectively impossible until you decide to begin working on it.

It’s zero if nobody actually says anything. The legislature has the power to reign in the president. They only have to threaten a bipartisan impeachment.

Impeachment of Kristi Noem could be more likely to succeed though.

Even if impeachment is off the cards, is it impossible to imagine that there could be any sort of impact from Republican lawmakers hearing Republican voters that, or other things are not what they voted for or want?

Impeachment is the wrong tactic at this moment. Eroding support of the less hardline members of the party is key. Call your reps and say I didn’t sign up for this: [specific list of things]