On further reflection, I do recall a story of Republican staffers denying access to obvious disrupters (as is the right of ANY staff management), but that is completely apples v. oranges to placing shills in the audience to propagandize.
Who writes this stuff?!
Parsing.
“and likened the practice to past campaign appearances by President George W. Bush, from which protesters have been barred.”
For the sentence to be grammatically correct, it would be...
“from which protesters HAD been barred.”
The word HAVE indicates a meaning of “from now on”.
It would appear the writer of that ‘line’, or speaker, had a little ‘slip of the tongue’ and was mentally referring to their own ‘plans’ to bar those they would deem as protesters.