If the polls look bad in November, I'd guess the most likely thing he'll do is declare some kind of emergency and try to shut down the election.
I don't know what the odds are that it would happen, but I'd put that as the top possibility. He knows what happens if he loses both chambers. I think he'd do literally anything to avoid it.
This Is How Trump Is Already Threatening the Midterms
WIRED
https://www.wired.com › Politics › Donald Trump
22 hours ago — WIRED surveyed the ways the Trump administration is working to manipulate this year's midterm elections.
The SAVE act and nationalizing elections.