Flip-Flopping All The Time
This 1994 video of Dick Cheney outlining, presciently, what would happen if the U.S. invaded Iraq has been making the rounds. And yes, it's pretty absurd that a person who made these salient points could then ignore them a decade later.
But, let us be contrarian for a second. How many Democrats were for using U.S. troops for peacekeeping in Yugoslavia? Most of them You could probably find some great videos of prominent Democrats saying how important it was for the U.S. to use its power to remove an evil dictator, and that a safe Europe meant a safer America, etc. etc. At the same time, you might remember Republicans were pretty pissed off about American lives being put in danger for a country half-way around the world. Dig up those tapes, and everyone will look stupid.
In the end, its important to realize that, no matter how cynical it sounds, there are very few politicians in either party who are willing to put their own ideology over party concerns and the hopes of reelection. No one cares about a consistency of political theory. If one party does something, the other must oppose, no matter if this opposition contradicts anything they've said or done in the past. It makes it hard to hold them to anything.