The lift that presidential candidates usually get in polls taken during or just after political conventions often doesn't say much about whether these events will have any lasting impact. Frequently, the boost in the polls for a candidate who has had a week of mostly positive publicity -- as George W. Bush has received this week -- disappears within a few days. But in some cases, the convention represents a real turning point in the campaign, producing a shift in voter opinions that carries through until Election Day. The problem is that there is no way of knowing at the time whether we are watching a soon-to-be-forgotten blip, or the beginning of a boom.
Four years ago, Bob Dole enjoyed a bounce after an uneventful convention in San Diego. But his boost in the Newsweek poll lasted no more than a week. Similarly, in 1992 President Bush benefitted from a short-lived rise in national voter surveys, despite the fractious convention in Houston, which was regarded by most analysts as divisive and destructive to his campaign. (See chart.)
Bill Clinton's increased support in polls taken after the 1992 convention, as shown in the trend line of the CBS News/New York Times surveys, represents one of the best examples of a bounce that signals an enduring turnaround in voter opinion. So too did the improvement of then-Vice President Bush, who turned a small deficit in Gallup polls before the 1988 GOP convention into a lead he never relinquished. Perhaps surprisingly, President Clinton got no lift from his 1996 convention, but he would go on to trounce Dole, who did get a bounce.
So even as the polls roll in over the next few days it will not be immediately apparent if they will be remembered as a blip, boom -- or bust.