Yes. Mitt is going to win regardless. The chance of a challenge from the right is unlikely and would be costly for Mitt. Mitt agrees to play nice for trumps endorsement. Not thrilled but it’s practical.
Trump should just have remained silent.
This isn't such a departure for Trump - after all, he did support Luther Strange over Roy Moore in the Alabama primary. My guess is that Trump is now even more reluctant to back an anti-establishment primary challengers because of the whole Roy Moore fiasco in Alabama.
I dislike Romney so I'm not happy about this either, but chances are we'd get stuck with Romney in the Senate regardless. Alternatively, if by some miracle he lost the primary to a more controversial conservative, there's always a risk of a Democrat winning what ought to be a solid GOP seat.