Buchanan established his through his 1992 primary challenge to George H. W. Bush. He won no states and few delegates, but inflicted serious damage on the president with a strong (near 40 percent) showing the New Hampshire primary and emerged as the uncontested leader of the G.O.P.’s economic nationalist wing.

At the same tine, Buchanan’s vitriolic brand of cultural conservatism and isolationist foreign policy tendencies marked him as a frightening figure to Middle America—and to a large chunk of the Republican Party. He had a big base, yes, but he also scored alarmingly high negative ratings in polls.

The benefits and limits of this profile were evident in his follow-up White House bid in 1996, when—in very crowded fields—Buchanan nearly won the Iowa caucuses with 23 percent (just behind Bob Dole’s 26 percent) and did prevail in New Hampshire with 29 percent. Very briefly, Buchanan was regarded as a legitimate threat to wrest the nomination, but then reality took hold: As the field thinned, his numbers refused to budge, while Dole, his surviving opponent, saw his support swell…

Given the trajectory of her overall poll numbers, that trend will probably intensify in the months ahead: More and more Republicans seem to be realizing that nominating Palin would, as John McCain’s old campaign manager put it, be “catastrophic” for the G.O.P. This means that, if she does run (and it’s certainly possible she won’t), she’ll be a contender in Iowa and some other early states—and she may even pull off a few wins. But once it’s down to her and one other candidate, the party will unite to stop her.