Suddenly, the principal presidential campaigns in the United States are having second thoughts about third-party candidacies.
Unlike the Canadian political system, where several parties are well-established and well-subscribed, the American political system has been so dominated for a century and a half by the Republican and Democratic parties that ordinarily barely a thought is given to outside parties – and even when, as in 1912, there were multiple significant entries on the presidential ballot, these entities inevitably are described, almost always dismissively, as "third parties." But as the struggle between Hillary Clinton and Donald Trump tightens – the closely monitored RealClear Politics polling average now has Ms. Clinton ahead by less than a percentage point – the significance of outside candidates, especially Gary Johnson of the Libertarian Party, is becoming clearer.
"Gary Johnson is in a position to swing the election," Patrick Buchanan, whose presence in the 2000 contest helped push the election into an agonizing 36-day overtime, said in an interview.
Late last week, the Commission on Presidential Debates announced that the two major outsiders – Mr. Johnson, the former governor of New Mexico, and the physician and environmental activist Jill Stein, the nominee of the Green Party – would not be included in the televised sessions that begin next week.
But that does not mean that Mr. Johnson and Dr. Stein do not have the potential to disrupt the election, perhaps even to affect its outcome.
"Really, Hillary Clinton is running against Jill Stein and Gary Johnson," said John Hanley, a political scientist at Duquesne University in Pennsylvania, one of the most competitive swing states in this election. "They provide the margins of victory. They're the spoiler candidates – and votes for them could really matter."
These "spoiler candidates" did matter in 2000, when ballots were re-examined carefully and recounted constantly in Florida, which held the balance of power between vice-president Albert Gore Jr. and governor George W. Bush of Texas, who was awarded the White House only after the U.S. Supreme Court intervened. "The Florida votes I took from Gore and the people who spoiled their ballots by voting for the two of us created chaos," Mr. Buchanan said.
These outside candidacies contributed to the upheaval not only in Florida but across the country, as well.
"My votes, while small, cost Bush badly," Mr. Buchanan said, and in fact Mr. Buchanan's vote harvest would have tipped the balance for Mr. Bush in Wisconsin, Oregon and Iowa, possibly rendering the Florida spectacle irrelevant. Mr. Buchanan captured a mere 1,392 votes in New Mexico – enough to swing the state from Mr. Gore to Mr. Bush in a very close contest and deliver five coveted electoral votes to the Texas governor.
The same is true, in reverse, in New Hampshire, where consumer advocate Ralph Nader's vote would have given the state to Mr. Gore – and sent the Tennessean rather than Mr. Bush to the White House.
Mr. Johnson and Dr. Stein were denied podiums at the Sept. 26 presidential debate because each failed to clear the 15-per-cent threshold the bipartisan commission established for participation. Both are under 10 percentage points in most voter surveys. Mr. Johnson, the stronger of the two candidates, has indicated that he hopes his poll support will grow sufficiently in the next several weeks to qualify for the second debate, on Oct. 9.
The political appeal of the two outsiders is being watched extremely carefully, especially by Ms. Clinton. Her campaign strategists worry that millennial voters who otherwise might side with her, may be so repelled by this year's sordid campaign that they may vote for Mr. Johnson or Dr. Stein.
That is a legitimate concern. A Quinnipiac University poll in Iowa showed that, together, Mr. Johnson and Dr. Stein have more support than either of the major candidates among voters 18 to 34 years old. Mr. Johnson himself is in a virtual tie with Ms. Clinton among those voters in that state, which gave Barack Obama, the Democratic candidate, a decisive victory, and its six electoral votes, four years ago.
That is why the Clinton campaign has mobilized Democratic Senators Bernie Sanders of Vermont and Elizabeth Warren of Massachusetts, both of whom appeal to millennials, and dispatched them to campaign events in swing states.
The latest New York Times/CBS News Poll showed the two major candidates with 42 percentage points each – leaving Mr. Johnson at eight percentage points and Dr. Stein at four percentage points, with only 2 per cent of likely voters undecided. The two outside candidates fare better when registered voters rather than likely voters are tallied, with Mr. Johnson's support inching up to 11 percentage points.
No one knows for sure where the Johnson and Stein votes would go if the major candidates mount offensives to lure their supporters away, nor is there a consensus about which major candidate is damaged the most by the presence of Mr. Johnson and Dr. Stein in a four-way race.
"It's not clear who Johnson takes votes from," said Mr. Buchanan. "He may take moderate Republicans from Hillary – but he could take voters from Trump in New Hampshire." But this much is known: If Mr. Johnson and Dr. Stein retain their voter strength, neither Mr. Trump nor Mrs. Clinton will need anywhere close to 50 per cent to win the election – a development that would substantially help Mr. Trump, whose path to the White House is generally regarded as more difficult than his rival's. A chilling reminder for Ms. Clinton: Her husband took the presidency in 1992 with only 43 per cent of the vote – a winning margin only because Texas billionaire H. Ross Perot, running a third-party campaign, won 19 per cent of the vote.