Ironically, the surest cure for the self-indulgent insanity of the current Republican Party would be a serious external threat.
Walt argues that the fringes of the Republican Party are creating chaos because the US is so safe right now. When there is an actual threat to the country's stability, the country pulls together and anyone who seems to challenge national unity is seen as an enemy.
But when nations are feeling secure from external dangers, both citizens and politicians are freer to indulge ideological whims or to pursue self-serving agendas of their own, because the body politic won't see these actions as undermining national unity or threatening national security. And that's at least partly why a yahoo like Cruz can get away with what he's doing.
Walt then asks, isn't there a real threat of terrorism. Isn't that why there is a Patriot Act and an expanded NSA? His response is "Nope" and this:
Sure, foreign-policy experts like me love to talk about the implications of events in far-flung regions, but that's mostly to give ourselves something to do and to remind everyone that We're Really Important.