After Humphrey lost to Richard Nixon, the Democrats appointed a commission led by Senator George McGovern of South Dakota to revise the rules of candidate selection. In the future all states would hold primary contests; whoever won a majority of the delegates would automatically win the nomination. In subsequent years these rules have been tweaked to make sure that certain demographic groups are given disproportionate (or proportionate, depending on one's point of view) weight in delegate selection. The kinds of people who sit on the convention floor now are greatly different from the party bosses, mayors, senators and governors of yore. They are younger, more urban, more affluent, more female and more black. Many fewer have ever actually campaigned for office on their own.

But the matter is even more complicated than that. When one speaks of Democratic "primaries" one is really referring to two quite different processes. One is an election in which all registered Democrats are allowed to go to the polls to cast their ballots for one of a number of candidates. The other, however, is a caucus, in which those Democrats so motivated can go to the equivalent of a town meeting somewhere in their state and, by voice or hand vote, opt for one of a list. Needless to say, this process puts a premium on ideological fervour and sensitivity to group pressures. Nonetheless, Democrats in a surprisingly large number of states hold caucuses rather than real primary elections; one of them is Iowa, which holds its contest first, in early January. As it happens, Iowa has the most left-wing Democratic party in the United States (its Republican party is also among the most right-wing). In choosing Obama over Hillary Clinton earlier this year, the Iowa Democrats made him a star overnight. His campaign suddenly picked up speed - and unleashed oceans of money from New York and Hollywood, as well as from thousands of small contributors on the internet, a tide that eventually sustained him to victory.

Mrs Clinton has argued, with some justification, that she won many of the primaries where voters went to the ballot box, whereas Obama tended to win caucuses, where the more extreme (or "out of touch") elements of the Democratic party tend to prevail. She has also pointed out, quite correctly, that most of the primaries she won (Pennsylvania, California, Ohio, New York) are far richer in electoral votes than the states where Obama typically prevailed. If Obama should lose to John McCain there will be pressures - particularly from the camp of the former president's wife - to revisit the way primaries are organised. Presumably Mrs Clinton would return to take advantage of such changes for the 2012 election cycle - after all, she really has nothing else in her life to do.