Contrary to the views of some, he has one, and Peter Feaver has found it:
It is a worldview that recognizes the benefits — to the United States and to the world — that has come from American global leadership.
It is a worldview that tempers American exceptionalism with a recognition of the universalism of American ideals — that is, Ryan recognizes that America is expected to bear burdens that other states do not, and also recognizes that the American idea has an appeal that other national founding ideas do not.
With a little digging, one could find echoing quotes from almost every president since Lincoln.
It is not triumphalistic; Ryan acknowledges limits to American power (as every president has done). It recognizes the need for prudence: In a brief section on Saudi Arabia, Ryan carefully navigates the tricky shoals of how to work with a longtime partner that does not share our values.
Perhaps its greatest appeal is the way he twins pessimism and optimism. Ryan paints a very pessimistic (albeit realistic) picture of the trajectory the country is on. And Ryan paints a very optimistic (and hopefully realistic) picture of the trajectory the country could be on, if we got our fiscal house in order.
Feaver mentions that Ryan’s worldview might bother someone like Stephen Walt, but this should hardly disqualify Ryan from consideration for a position of national leadership. For one thing, there is a lot about Ryan’s worldview that should appeal to realists like me; after all, Ryan acknowledges that there are limits on American power (though he knows that American power outstrips that of other countries). For another, Walt certainly does not speak for all realists. And finally, Walt isn’t much of a realist these days. Indeed, he isn’t much of a scholar at all–at least when it comes to his blogospheric writings.