That sounds like wishful thinking on Sununu's part. No other republican can give people permission to be openly racist. Even DeSantis is focused on homophobia and transphobia. He is passively racist. The base wants a snarling sadistic overt racism, and the orange guy is the one who delivers the goods.
Alas, I fear the governor is wrong. Trump will most likely be the GOP nominee.
Only way for Trump to lose the nomination, even if he is indicted, is a two man race. Most of the GOP primaries are winner take all. Trump will get 35% of the vote, no matter what. In a large field, he gets the nomination. Trump's negatives are higher than 35%, over 50%. At this point he can't win general election. I fear Sununu is right.