It was a familiar sight, earlier this year, at watering holes and social-circuit locales in the nation's capital.
Amidst sexual-harassment allegations that had made interparty relations even more toxic than usual, Liberals would be on one side of the bar and New Democrats the other. Plainly unable to stand the sight of each other, they would go out of their way to avoid any contact whatsoever.
It is possible that, by this point, they might be capable of some perfunctory small talk. But given all the speculation about how the two erstwhile opposition parties might work together if there is a minority government after Monday's election, it is hard not to wonder how capable they are of setting aside their mutual animosity.
No doubt, most of the people who cast ballots for them will want them to do just that, should the situation demand it. Most Canadians who vote NDP would rather see Justin Trudeau in the Prime Minister's Office than Stephen Harper. Lots of Liberal supporters feel the same way about Tom Mulcair, relative to Mr. Harper, though given what the polls are saying, that's a bit of a moot point at the moment.
The people at the highest levels of the parties battling for the centre-left, though, are a different story. If you caught them at a frank moment, senior New Democrats might concede that they would prefer a Conservative government to a Liberal one, and senior Liberals might offer a similar sentiment if the roles were reversed.
To the extent this dynamic has been noted over the course of this election campaign, it has mostly been chalked up to (very valid) political calculus.
After finally establishing themselves as the main alternative to the Tories last election, the last thing the NDP wants to do is help the Liberals go back to being the natural governing party. The Liberals quietly conceded, at the start of the campaign, that their biggest imperative was to get ahead of the NDP, lest they lose their reason to exist.
But it is not just about game theory. Because easy though it sometimes is to forget, politicians and the people who work for them are human beings with real emotions, and sometimes those can get in the way of public interests, or their own.
New Democrats have a visceral dislike of Liberals, whom they consider cynical and smug and untrustworthy opportunists, at the best of times. (A common refrain: "With Tories, at least you know where you stand.") That's amplified by anger at the prospect of somehow ranking behind Justin Trudeau, whom they perceive as a lightweight epitome of Liberal entitlement. The lack of respect for Mr. Trudeau has been evident in many of Mr. Mulcair's public performances, particularly in leaders' debates, and all the more so in private conversations with some of his officials.
The Liberals may not have quite the same disdain for Mr. Mulcair, personally. But they tend to consider New Democrats a bunch of sanctimonious hypocrites – pious in public, at least as cutthroat as the Conservatives behind closed doors.
In a matter of a few days, the Liberals and NDP might have no choice but to try to set all that aside. Both Mr. Trudeau and Mr. Mulcair have said they wouldn't prop up a minority government under Mr. Harper, and backtracking on that could be political suicide. If the Liberals win a plurality of seats, a lack of at least modest co-operation would be even harder to defend, and neither party can really afford to go into another election campaign imminently.
But the last time that a Liberal minority government in this country had to rely on a third-place NDP to keep it afloat – in Ontario, between 2011 and 2014 – there was near-constant drama and dysfunction. By the time Dalton McGuinty left office, a year-and-a-half into this relationship, he and NDP Leader Andrea Horwath proved all but incapable of getting along. It didn't take long after Kathleen Wynne took over for Mr. McGuinty before her relationship with Ms. Horwath was even worse.
Perhaps Mr. Trudeau and Mr. Mulcair – or a different NDP leader, depending on this election's fallout – will prove more able to get over themselves. Those wishing for something reasonably stable out of this vote might have to hope so. But nobody who has spent much time around people from either of their parties could be too confident about it.