“There are no more arbiters of truth,” former White House Press Secretary Robert Gibbs told the Politico website. “So whatever you can prove factually, somebody else can find something else and point to it with enough ferocity to get people to believe it. We’ve crossed some Rubicon into the unknown.”

Like so many of the genuinely disjunctive moments in American history, this Rubicon flows with both old and new currents.

The new, of course, is the way in which the alternate realities of the Internet’s fringes and brutally partisan talk radio empower the political culture of assertion and denial to which the birthers belong. It’s a characteristic they share with a significant slice of the “tea party” movement, which advances not just its own version of contemporary America but a willed, faith-based version of our history as well…

A political climate in which people shout at each other presents one set of problems; one in which people simply talk past each other in mutually unintelligible languages is something new and alarming.