Professor Ribstein has been noting the increasingly polarized nature of political debate in America, best reflected by the tendency of many critics of President Bush to eschew fair criticism for ad hominem attacks.
Although Professor Ribstein is correct that Bush-bashing is prevalent, I’m not certain that this is all that unusual. American Presidential campaigns have often been ribald affairs in which strident supporters of one candidate have characterized the opposing candidate as evil, immoral, moronic, or worse.
For example, the campaigns immediately after George Washington‘s terms in office were no picnic, and later, Andrew Jackson‘s opponents used many of the same tactics that the Bush-bashers use now. Even Abe Lincoln endured a good deal of these types of attacks in the 1864 election, and more recently, Barry Goldwater in 1964 and Richard Nixon in 1972 were often characterized as the epitome of evil by their opponents. Particularly during the 1980 election, opponents of Ronald Reagan often portrayed him as an idiot mouthpiece controlled by others.
However, the WSJ’s ($) Alan Murray in his Political Capital column this week may point to the reason that the Bush-bashers are using this particular technique during this Presidential campaign:

To an unprecedented degree, Americans already have decided how they are going to vote in November. Polls differ, but all suggest that between 43% and 45% of voters plan to vote for George W. Bush and won’t give any consideration to John Kerry, and an equal percentage plan to vote for Sen. Kerry, and won’t give any consideration to President Bush.
That leaves just 10% to 15% of voters who say they remain uncertain about how they will vote. And Republican pollster Bill McInturff says his research shows even most of the undecided voters are less malleable than the label indicates. “The polarization is exceptional,” says Democratic pollster Peter Hart. “Even the independents break down into pro-Bush and anti-Bush groups.” Kerry strategist Mark Mellman goes further: “All the evidence suggests we are fighting over less than 10% of the electorate, and probably less than 6%.” Says Mr. McInturff: “I’ve never seen anything like this in my 25-year career.”

Could it be that the Bush-bashers have concluded that their approach is the most effective means by which to persuade a majority of this 10% undecided group? Or is it simply a means by which to maintain the passion of the base of Bush opponents to ensure that base turns out on election day? Or both?
Update: Professor Ribstein notes the difference in the nature of the current Bush bashing with previous President bashing.