Which Senate race are Republicans more likely to blow?

[Vosem]

I'm going to go ahead and agree with you. Some early indicators of Biden's approval rating are that he's holding up poorly in the Southwest. The possible Republican contenders in Arizona (Brnovich, Masters, Landau, and Ducey reconsidering are commonly cited) all seem pretty strong, while the Republicans in North Carolina are coalescing around a Governor who lost reelection in a good year and an accidental Congressman who won his first primary with 20%.

(To be clear, I think NC-Sen is a likelier Republican win than AZ-Sen because AZ-Sen has a Democratic incumbent. But which race are Republicans likelier to blow, ie, lose because the nominee says or does something stupid or doesn't put enough effort in? NC actually seems a hair likelier.)