If it happens, it will be about as successful as the GOP's attempt to defeat Barbara Boxer in 2010. There will be a few polls showing a very close race only for Cruz to win by at least 8 points on election day.
Not Boxer, but Murray. TX is not that Republican as CA is Democratic.
Honestly WA is probably more Democratic than TX is Republican at this point. I'd put this in the same category as Heinrich's 2018 race.
I guess it's likely to be "about as successful as the attempt to defeat Boxer" in the sense that both are ultimately failures, though.