Trump has stated he is pro-2nd amendment and for gun ownership so many times in the public eye it did make me wonder why Cruz would say such a thing. Surely he had to know Trump's position on this. If not, that's a huge oversight.
Trump backed the assault weapons ban in his book.
Trump’s 2A position is clearly stated at the following link.
https://www.donaldjtrump.com/positions/second-amendment-rights
Because Trump has said a lot of things. And then he said the exact opposite of those things. If someone tries to hold Trump accountable for something he says, a Trumpophile calls the accuser a liar simply because there is another Trump quote contradicting the first Trump quote. Its why Jimmy Carter called Trump “malleable.”
Trump has stated he is pro-2nd amendment and for gun ownership so many times in the public eye it did make me wonder why Cruz would say such a thing. Surely he had to know Trump’s position on this. If not, that’s a huge oversight.
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Trump has a concealed carry permit (CCP) and carries a gun.
Was there any other Republican on that stage, that we know of, who has a CCP besides Trump?
My husband and I have one. Those that hace CCP permits are the most pro-2nd amendment group I can really think of. And CCP’s are NOT for hunting.

Cruz is a liar.
The reason I bring that up is in these last two unhinged days Cruz has lied about Trump's stance on the 2nd amendment and Rubio's very strong pro-life views. That could be too much for them to forgive and forget.
When Cruz gets caught in an ill-advised statement or action, he doesn't back off. He just gets nastier. It isn't pleasant to observe.