This about sums it up (from today's LA Times editorial):

The technique President Bush is using against John F. Kerry was perfected by his father against Michael Dukakis in 1988, though its roots go back at least to Sen. Joseph McCarthy. It is: Bring a charge, however bogus. Make the charge simple: Dukakis "vetoed the Pledge of Allegiance"; Bill Clinton "raised taxes 128 times"; "there are [pick a number] Communists in the State Department." But make sure the supporting details are complicated and blurry enough to prevent easy refutation.

Then sit back and let the media do your work for you. Journalists have to report the charges, usually feel obliged to report the rebuttal, and often even attempt an analysis or assessment. But the canons of the profession prevent most journalists from saying outright: These charges are false. As a result, the voters are left with a general sense that there is some controversy over Dukakis' patriotism or Kerry's service in Vietnam. And they have been distracted from thinking about real issues (like the war going on now) by these laboratory concoctions.