Steven Hayward asks in his latest National Review column: Why have recent Republican running mates inspired such passionate attacks from Democrats and their ideological allies?

The reason for the vitriolic reaction to Sarah Palin four years ago was simple: She threatened to shatter a pillar of the Left’s identity politics by contesting its monopoly on “women’s issues.” Ryan represents a triple threat. Most obviously, his fiscal plans threaten the Left’s entitlement mentality, and his personality and charisma may hive off the youth vote. But the deepest fear is that Ryan will challenge directly the core philosophy of today’s so-called progressivism.

Liberals say they are delighted with the Ryan pick because they can now run the “Mediscare” campaign, but they are not being entirely honest. Beyond the fiscal debate, Ryan can expose progressivism’s unreflective rejection of the principles of the American Founding.

The old progressives were an oddly mixed bag; the movement’s roots could be seen in both parties at the time. On the one hand, people such as Woodrow Wilson and John Dewey explicitly rejected the natural-rights philosophy of the American Founding in favor of an admixture of Hegelian and Darwinian “pragmatism,” according to which “progress” is essentially the growth of the state. Many progressives thought our Constitution was obsolete, though they were able to fix that problem by bringing it to life. These beliefs remain the philosophical core of modern liberalism, though very few liberals, now that Richard Rorty is dead, can puzzle out the deep presuppositions of it anymore. Instead, today’s progressives hold a lazy presumption that progress entails politicizing every problem without end. This is the aspect of progressivism that Ryan most directly challenges.