On The Late Show With Stephen Colbert, host Stephen Colbert played a hilarious "debate" consisting of videos of Donald Trump showing how he's radically changed position on a variety of issues--sometimes with only weeks in between the time the videos were shot.
It's pretty eye-opening:
Given that the oldest video in this montage (minus, of course, old endorsement commercials) is from December 2011, where he praises Megyn Kelly, I'd say that these are all fair for Colbert to use. Trump's praise of Hillary Clinton as someone who is "doing a good job" a mere three years ago is not something that can or should be ignored by the electorate. Mitt Romney was absolutely crucified for his changes of heart on issues--and this was an evolution that occurred over a matter of years, not weeks. It's ludicrous to give Trump a pass.