Herman Cain’s recent stumbles over substantive issues have a way of making Rick Perry seem like the Stephen Hawking of politics. In the midst of a softball CNN interview last week, he appeared to abandon his no-exceptions anti-abortion stance. The former pizza magnate also said that he hypothetically might swap terrorists held on Guantanamo for an American soldier—and then embarrassingly backtracked during the Las Vegas debate. Asked about his foreign policy orientation on Meet the Press, a baffled Cain replied, “I’m not familiar with the neo-conservative movement.” And listening to Cain constantly struggle to explain why his regressive 9-9-9 plan would not raise taxes for most Americans is a reminder of the punch line of an old joke: “Do you believe me or your own eyes?”

Small wonder, therefore, that the likely story arc for Cain is that doubts about his candidacy continue to multiply until he is on a glide path for a primetime hosting slot on Fox News. As Joshua Green reported in Business Week, Cain is carefully keeping his post-campaign options open by continuing his paid speeches (“I have not raised my prices”) and hawking his latest autobiography, This Is Herman Cain! My Journey to the White House.

This is how presidential vetting traditionally works. The press pack pounces on the logical fallacies in a candidate’s positions and the shakiness of his resume. Party elites and top fundraisers then decide, if they have not already, that any candidate subjected to this kind of non-ideological media assault is unelectable. And eventually voters—especially when the calendar moves beyond activist-dominated Iowa—get the message that they are trying to elect a president and not merely thumbing their noses at the establishment.

As a result, neither party has nominated a patently unqualified candidate for president in more than a century. But ever since voters in primaries and caucuses replaced party bosses at the center of the nominating process, there has always been a theoretical risk that the unofficial vetting system could break down. And this year, in particular, there’s a substantial case to be made that all bets and vets are off.

HERMAIN CAIN HAS illustrious predecessors—other outlandish Republican presidential contenders who have had their Icarus moments in the sun. At the end of 1987, Newsweek ballyhooed televangelist Pat Robertson’s “invisible army” in a story headlined, “Is It Time to Take Pat Seriously?” After Pat Buchanan narrowly won the 1996 New Hampshire primary, a newspaper columnist named (whoops!) Walter Shapiro declared, “He should be considered the presumptive frontrunner.” Twelve years ago this month, New York Times columnist William Safire predicted that flat-tax troubadour Steve Forbes would give George W. Bush “a run for both of their money.” And an October 1999 Washington Post story reported that the Bush camp “has been almost obsessed with Forbes’s candidacy.”