As catnipman out so well:
“The problem is if he knew about it, then his judgement is bad; if he didn’t know about it, then he is unable to manage his own campaign, which throws doubt on his ability to manage the United States government.â€
That is an interesting observation.
If this were a pattern of behavior of his staffers, you might have a point.
A one-off gaffe like this does not reflect on the enire campaign staff or Cruz.
Using the same standard you refer to: Admiral Poindexter misleading Col North (Iran-Contra) means Reagan was unable to manage his people. Clearly, this was not the case. There are many other cases where people are people and do not act responsibly and that is why people get fired.
Absent proof this was approved strategy by the campaign and not the actions of one guy, I will withhold judgement.