PHILADELPHIA - A wise old political veteran once observed that Americans rarely, with the exception of national heroes, make their voting decisions on a positive basis.
''They vote against one candidate, not necessarily for the other,'' he explained.
A classic example of this was in the 1980 presidential race when obviously unhappy voters were tired of soaring inflation, record high interest rates and dwindling U.S. stature internationally and were ready to vote against Jimmy Carter.
They didn't know, however, whether they wanted to vote for a former movie star who many thought had play-acted through the governorship of California. It was up to Ronald Reagan to convince them he wasn't the far-right lightweight that Democrats said he was. He did this early in the campaign by moving decidedly toward the center in the first debate.
A more recent example occurred in 1992 when voters deemed President George Bush unsympathetic to their economic woes and voted against him and in favor of Bill Clinton, who had effectively exploited this negative factor.
The current presidential campaign seems to be shaping up in this classic fashion, with voters seemingly ready for a change but not all that sure of the Republican nominee, George W. Bush. It will be up to Bush to show Americans, particularly the 20 percent of unaligned and swing voters who will decide the outcome, that he would be a good, capable president with a vision for the future.
So far he seems to have been successful enough in allaying fears about his ability, maintaining a lead in polls that ranges from a low of 4 points to a high of 14 points. That lead is expected to narrow substantially if not disappear completely by the end of the Democratic National Convention in Los Angeles this month.
Then the real test will come for Bush.
Republican strategists expect Vice President Al Gore and the entire Democratic Party apparatus to launch a full-out attack to persuade voters that Bush is not up to the job and that his running mate, former Rep. Dick Cheney, is from the GOP's far-right fringe and is dangerous. Democrats will hammer, as they have for two weeks now, on Cheney's conservative voting record as a House member 20 years ago.
''Gore and his people will run a slash-and-burn campaign,'' former GOP national chairman Haley Barbour predicted to reporters here. ''He has the first team of nasty boys running his campaign.''
How well Bush withstands this onslaught, Barbour said, will determine ''an extremely close election.''
While Barbour and others may be painting an exaggerated picture of Gore's expected campaign, there is little question that the vice president, who has trouble getting beyond 47 percent in the polls, ultimately will have to become more negative.
Bush himself must stay on message, the experts believe, resisting the temptation to respond to attacks. If he does attack Gore, it should be strictly on the issues, so, according to Barbour and others, it doesn't appear to be negative. This, of course, doesn't mean that Bush won't ''counterpunch'' sustained attacks by his opponent, but probably will use Cheney as the ''bad cop'' as he did here Wednesday when Cheney sounded about the only notes of the convention critical of Gore and President Clinton.
Surveys show that Bush has had great success with an issue-oriented campaign. He is within a few points of Gore on the core issues of education and Social Security-Medicare, long an exclusive province of the Democrats.
The GOP nominee also leaves this convention with a party more united than it has been since Reagan's re-election in 1984. Internal research reveals that 90 percent of party regulars are behind him, putting aside differences over a variety of social issues to try to recapture the White House.
For Bush to come out ahead in November, social conservatives including the Christian Right will have to sustain their tolerance as he moves more toward the middle ground where this election will be decided.
Few candidates in recent memory seem as confident as Bush of his ability to meet the challenges. Certainly, Gore, who by all rights should be, isn't, despite being a part of an administration that has enjoyed an unparalleled economy
The vice president's hopes rest with his ability to convince the ''anti'' voters that it is Bush they must cast their ballots against.
(Dan K. Thomasson is former editor of Scripps Howard News Service.)