I can see Democrats been favoured in the House until 2032 (when the 2030 cencus kicks in) and the Senate until 2036 (Tester is not up in another Presidential year until 2036 and the GOP needs his seat to offset future loses).
But if Trump wins by 5 I don't think Democrats would do any better than 2018 in the House, but will take the Senate, since the GOP is currently unlikely to do well in senate races this year.
If Democrats get a trifecta at any time during those years, they have a serious opportunity to make some significant changes. With Manchin and Sinema gone, they will either eliminate or suspend the filibuster to pass the Freedom to Vote Act (establishing redistricting standards for the entire country) and admit DC as a state (possibly Puerto Rico as well).
