Jay Cost argues convincingly that “No serious Democratic official would dare challenge Obama for the nomination.” But Ralph Nader says that “I would guess that the chances of there being a challenge to Obama in the primary are almost 100 percent.” Nader says that challenger could be “an ex-senator or an ex-governor” or “an intellectual leader or an environmental leader.”

Both Cost and Nader can be right. There could be a challenger to Obama, but he (or she) wouldn’t be a “serious” opponent of the caliber of Robert Kennedy (1968) or Ronald Reagan (1976) or Ted Kennedy (1980). He would be more like John Ashbrook (1972) or Pat Buchanan (1992). But that’s not nothing. Ashbrook arguably helped keep the conservative flame alive in the age of Nixon, a flame that Reagan re-lit in 1976 and brought across the finish line in 1980. Buchanan’s campaign in 1992 was distorted by his own peculiar brand of conservatism. But his exposure of George H. W. Bush’s weakness probably helped induce Ross Perot into the general election contest, and both to some degree laid the groundwork for the Gingrich takeover and renewal of 1994. And of course the Tea Party challenges of 2010 were crucial to the liberation of the GOP from the legacy of the doldrums of George W. Bush’s second term.