Politicians in the United States will frequently bring forth members of the public to bolster their arguments at speeches or rallies, or even in Congress. For instance, Donald Trump recently called up a college student to emphasize his arguments for what he qualifies as freedom of speech. Sometimes these average citizens even say a few words, generally in support of the person who called them up.
This seems like a gamble, though, since the person might turn out not to be a supporter. They might even start talking even if they weren't asked to. Has anyone ever taken advantage of this forum to criticize the politician or party who invited them?