Generic Democrat polls are usually useless, especially this far out. But Cornyn stuck at 41% isn't a good sign for him. Lean Republican for now; probably closer to likely than tossup. But it's early and things can change.
Beto obviously made a huge miscalculation with his presidential campaign. Jumping back into the senate race now would make him look like a desperate officeseeker. That's why only 30% want him to run now.
Even though this poll seems flawed to me (how can there be that many undecideds?), I think that it is more likely than not that Cornyn will be held to a mid to high single digit margin in 2020. And it's also clear to me that O'Rourke would have been well poised to knock Cornyn off next year had he not launched his vain presidential bid, or if he had dropped out months ago. His last opportunity to pivot was back in August, but instead he decided to renew his presidential campaign.
