Some voters told reporters that they didn’t want Obama to run, let alone win, should his very presence unleash the demons who have stalked America from Lincoln to King. After consultation with Congress, Michael Chertoff, the homeland security secretary, gave Obama a Secret Service detail earlier than any presidential candidate in our history — in May 2007, some eight months before the first Democratic primaries.

“I’ve got the best protection in the world, so stop worrying,” Obama reassured his supporters. Eventually the country got conditioned to his appearing in large arenas without incident (though I confess that the first loud burst of fireworks at the end of his convention stadium speech gave me a start). In America, nothing does succeed like success. The fear receded.

Until now. At McCain-Palin rallies, the raucous and insistent cries of “Treason!” and “Terrorist!” and “Kill him!” and “Off with his head!” as well as the uninhibited slinging of racial epithets, are actually something new in a campaign that has seen almost every conceivable twist. They are alarms. Doing nothing is not an option.