For me it was a gaffe that he could not substantiate his assertion about the Mexican government.
He had about twice as much air time as anyone else. 11+ minutes while most had 6.5 minutes.
In thirty seconds? That's not enough time to substantiate anything....
Nor should he need to substantiate the assertion. It's been well known for years -- and reported by Fox and NYT long ago -- that the Mexican government produces and distributes pamphlets with advice on how to safely sneak over the border, how to evade BP, etc.