A 10th grader could tell that the word that should have been used was than rather than then. And, Liberals think they are so smart. 
The rally took place near where I live here in central Ohio, and the local news coverage was not bad: the bad-grammar airplane was shown only for a split second, so as "to be fair" to the Dems, I am sure!

And yes, most of my Latin students in the 6th, 7th, and 8th Grades would not have made that mistake!
Then does
not equal
than!