What will the presidential and downballot environments be? How exactly will they differ?
Well in Presidential elections they don't differ usually that much lately.
And neither will get 400+ E.V. which is the standard for "landslide", but here are 3 scenarios.
Scenario A. Lets say Trump wins the popular vote by around 4, which is the forming consensus, and if the GOP more or less copied that performance downballot I guess the following by region:
Spoiler alert! Click Show to show the content.
1. GOP picks up 1-2 seats somewhere in the West Coast states.
2. GOP picks up all 3 Nevada seats plus 1-2 somewhere in New Mexico and Texas.
3. GOP picks up 1-2 seats somewhere in the East Coast states.
4. GOP picks up 1-2 seats somewhere in the Midwest.
I guess the Democrats from all the gerrymandering and redistricting net 7 but lose at least 9 on the ballot box.
So the GOP House majority ought to be similar or slightly larger.
The Senate depends on Trumps victory margin in individual states, usually anything above Trump +10 with the right candidates will go GOP against Democrat incumbents, plus Nevada and Michigan recently don't give incumbents advantages.
If everything goes right for them, 56 seats max, but best case is always unlikely, 52-53 is a realistic result.
Scenario B. Lets say Quinnipiac is right and Democrats win the White Vote while losing the Hispanic vote.
Spoiler alert! Click Show to show the content.
1.House Democrats would probably pick up 5-6 seats in the Midwest.
2.House Dems pick up 1-2 in Colorado and Utah.
3.House Dems pick up 2-3 somewhere in the East Coast.
A small House D majority slightly larger than their 2020 one.
Senate Democrats keep it 50-50.
Scenario C. Lets say it's a tie.
Spoiler alert! Click Show to show the content.
House GOP would lose 1-2 somewhere in Colorado, Utah, Nebraska, or Virginia.
House Dems get a small majority about the same size as in 2020.
Senate GOP gets 51-52 seats.
Summary:
Because the GOP is doing so well with minorities with respect to whites and because states are so gerrymandered, it's difficult to change the House math that much until voting moves flip gerrymanders.