Kirk often warned that left-wing residents from “failed” blue states (like California) relocate to conservative states and “ruin” them politically. For example, he has cautioned that California transplants could turn Texas or Arizona blue.

https://generik.substack.com/p/fact-checking-charlie-kirks-awfulness

So what I've gathered he didn't say it won't happen but rather was afraid it would.

Edit: also, the context is people moving there not people turning their back to GOP which is what happened from my understanding