I was reading this article on how Reagan won the Cold War and it got me thinking about how and why it is that only those who previously held views on one extreme can implement policies on the other extreme (another way of saying this is that a politician on one side of the political spectrum is better able to implement the policies of the other side). Reagan is a good example of this.
He came into office the consummate Cold Warrior, spending money on defense like a drunken sailor and spouting very hawkish rhetoric about the Evil Empire of the Soviet Union. But in his second term he negotiated myriad arms control agreements with the Soviets, even offering to eliminate nuclear weapons entirely. If someone like Carter or Mondale (who has the unique distinction of being the only politician to lose an election in all 50 states [losing 49 states to Reagan and recently losing a Senate race in his home state]) had tried to follow this policy of detente, he would have been eaten alive by conservatives. Because Reagan had already established his bona fides as a hawk, he was able to act like a dove.
This can be very irritating for those on the same side as the perpetrator, like when liberals got angry at Clinton for signing the welfare reform bill. So the paradox is that sometimes the only way to get something relatively extreme enacted is for the other side to do it. Sad but true.