Just because I don’t think much of Trump, for you then to jump to the conclusion I must be, to use your term, “an open-borders guy”—that indeed does not follow.
I said, At least Trump is not Hillary. You said, That is all he has going for him.
If you are indeed not an "open-borders guy," then it does not follow for you to have said simply, That is all he has going for him.
What would follow would be, That is all he has going for him, PLUS he wants to secure our borders, as do I!