Coburn’s implicit rationalization for far-right fanatics bearing arms at presidential events — the government makes them do it! — cannot stand. He’s not a radio or Fox News bloviator paid a fortune to be outrageous; he’s a card-carrying member of the United States Senate. On Monday — the day after he gave a pass to those threatening violence — a dozen provocateurs with guns, at least two of them bearing assault weapons, showed up for Obama’s V.F.W. speech in Phoenix. Within hours, another member of Congress — Phil Gingrey of Georgia — was telling Chris Matthews on MSNBC that as long as brandishing guns is legal, he, too, saw no reason to discourage Americans from showing up armed at public meetings…

No, the biggest contributor to this resurgence of radicalism remains panic in some precincts about a new era of cultural and demographic change. As the sociologist Daniel Bell put it, “What the right as a whole fears is the erosion of its own social position, the collapse of its power, the increasing incomprehensibility of a world — now overwhelmingly technical and complex — that has changed so drastically within a lifetime.”

Bell’s analysis appeared in his essay “The Dispossessed,” published in 1962, between John Kennedy’s election and assassination. J.F.K., no more a leftist than Obama, was the first Roman Catholic in the White House and the tribune of a new liberal order. Bell could have also written his diagnosis in 1992, between Bill Clinton’s election and the Oklahoma City bombing. Clinton, like Kennedy and Obama, brought liberals back into power after a conservative reign and represented a generational turnover that stoked the fears of the dispossessed.