Bald faced lying back stabbers can appear very friendly and congenial. It's a practiced art, and some people are so good at it, they can fool the devil.
Perhaps Walker has had a true change of heart about Trump since he left the 2016 primary, but I can tell you that, at that time, he was as anti-Trump as any Democrat.
Find any articles that covered his withdrawal from the race, and you'll likely see the low down, rotten comments he made about Trump at that time. It was despicable.
Bald faced lying back stabbers can appear very friendly and congenial.
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Mitt Romney and Paul Ryan come to mind.