So the party came to Chicago with no clear choice. By one count, 18 credible Democrats were promoted for the nomination to one degree or another. And then there was Adlai Stevenson, the squeaky-clean governor of Illinois, whom Truman had unsuccessfully tried to entice into the race. After Stevenson dazzled the delegates with his welcoming speech ("Where we have erred, let there be no denial, where we have wronged the public trust, let there be no excuses. Self-criticism is the secret weapon of democracy. …"), the effort to draft him grew. After Chicago Democratic boss Jake Arvey persuaded Stevenson to put his name into contention, the mayors and governors closed ranks. Stevenson won on the third ballot.
In the years since, there have been plenty of conventions at which the result was contested, but it's hard to find a genuine example of political leaders brokering the convention to determine the nominee among themselves. At the 1960 Democratic Convention, for example, Chicago Mayor Richard Daley and Pennsylvania Gov. David Lawrence provided critical support for Sen. John F. Kennedy over Lyndon Johnson and also over Adlai Stevenson, Lawrence's political hero. But the Massachusetts senator had come to the convention with the lion's share of delegates, and he had demonstrated his political chops by winning seven primaries, including a landslide victory in the heavily Protestant state of West Virginia, reassuring fellow Democrats that he could be elected as a Catholic. Party bigwigs like Daley and Lawrence didn't broker the choice; they ratified it. As Theodore H. White wrote in his classic The Making of the President 1960, "As Caesar, after he had conquered Gaul, used the Gallic cavalrymen to mop up Pompey and the ensuing civil wars of Rome, so now was Kennedy using the big-city bosses to mop up Stevenson." (They don't write political journalism like that anymore.)
No party boss decided the raucously contested Democratic conventions in 1968 and 1972, either—both involved a straight-up clash of candidates and delegates. McGovern got to seat his winner-take-all California delegation in 1972 simply because he had more delegates. In 1976, when Reagan almost wrested the nomination from President Ford at the Republican Convention, it was the power of Ford's incumbency, along with his concessions to conservatives—dumping Vice President Nelson Rockefeller from the ticket, for example—that gave him his narrow victory.
What about the prospects for a brokered convention this time? Assume for a moment that Clinton wins big in Pennsylvania and then goes on to do well enough in the last set of primaries to erase Obama's lead in the popular-vote count. Imagine that she also leads Obama in head-to-head national polls and matches up better against John McCain. Then throw into the mix the likelihood that Obama still leads among pledged delegates.
This would seem an ideal scenario for a brokered convention—except, who are the brokers? Which political leaders can deliver pocketfuls of delegates? The short answer is, no one. The undecided superdelegates control exactly one vote each (or half a vote)—their own. The idea that a cohort of these folks will unify calls to mind the difficulty of herding cats. To be sure, dozens of House superdelegates will listen to House Speaker Nancy Pelosi, but the politics of their districts—or their key financial supporters—are likely to matter a lot more to them. As for National Chairman Howard Dean, his office comes with few if any powers of persuasion. Even its fundraising pales in comparison with the party's senatorial and congressional campaign committees, and Dean's political clout has so far proven nonexistent. Al Gore clearly has the respect of his party, but many of the brokered convention fantasies revolve around him as the ultimate nominee, not kingmaker.
In other words, if the Democratic Party finds itself gathering in Denver without an obvious nominee, the process of picking one will make the brokered conventions of the past seem models of efficiency. And even if you could somehow find the brokers, where would they gather? With all the ordinances and clean-air talk today, there's not a single smoke-filled room to be found.