Actually, this is risky for Trump. So far Trump and Cruz have played it well. They both know that they will need the supporters of the other when election day comes, they can’t afford to alienate the supporters of the other. So they have, so far, been respectful of one another and by extension respectful of one another’s supporters.
Trump is obviously worried that Cruz may come out on top and has decided to take him down. But he has to do it in such a way that Cruz’s supporters will see him as their substitute champion. Using this line of attack on Cruz may just backfire.
Almost everything Trump does seems risky at first.