There are two differences, I think, between liberals and conservatives when it comes to this sort of thing. The first is that the Democrats still believe that there are a few things that shouldn’t be politicized, while Karl Rove and his crowd thought absolutely everything should be. But there’s a more enduring difference than that. It’s about America’s role in the world and how it should exercise its power, and it goes back to the Cold War. Liberal Cold Warriors considered the dirty work of foreign policy a sad but unavoidable burden that history had placed on America’s shoulders. Conservative Cold Warriors as a group were more gung-ho and had no patience for that sort of temporizing.
This isn’t to say that liberals were right about everything and conservatives wrong—both were wrong, for example, about the need to defeat Ho Chi Minh. But there were indeed cases in which the liberal urge for restraint, I think we would agree, paid off: If conservatives of 1952-53 had had their way, for example, we’d probably have nuked North Korea and started a war with China. If you want to get highfalutin about it, a lot of this goes back to Reinhold Niebuhr, the leading liberal foreign-policy intellectual of his time, and a man Obama has openly revered.