The precise moment at which Thomas Mulcair became unfit to be prime minister of Canada is hard to pin down.

It arguably came in 2005, when his party adopted what has become known as the Sherbrooke Declaration — in which the federal New Democrats accept that is possible to break up the country with 50% plus a single, solitary vote. When the NDP’s own constitution requires two-thirds to be amended.

It may have come in late 2012, when the NDP leader refused to defend the flying of the Canadian flag at ceremonies at Quebec’s National Assembly. Instead, Mulcair sent out one of his crypto-separatist MPs, who snapped that the banning of the Maple Leaf was Quebec’s “own business.”

Or, it may have happened earlier this year, when Mulcair approved a move to rescind the Clarity Act, the 2000 legislation that governs the rules surrounding secession of a province. The federal NDP want to clear up unity “fairy tales,” he said at the time.

Most likely, however, Mulcair ceased to be a contender for prime minister sometime in April, when a book was published in Quebec suggesting the judges of the Supreme Court of Canada actually conspired against Quebec’s then-separatist government. In the book, La bataille de Londres, Quebec journalist Frederic Bastien claims Chief Justice Bora Laskin passed secrets to the Canadian and British governments on discussions between high court justices about the legality of constitutional repatriation.

Bastien also accuses former Justice Willard Estey of slipping confidential information to the British government in 1980. Never mind that an unprecedented Supreme Court investigation found no evidence whatsoever to validate Bastien’s claims.

Never mind that Laskin and Estey were not merely two great jurists — they were two of the greatest Canadians to have ever lived, and that they are not here to defend their good names. Never mind any of that. No, note this: When Bastien’s corrosive conspiracy theories were trotted out, Mulcair giddily seized on them, and demanded an inquiry. And, when he got one, he dismissed the results, because they favoured Canada.

Said Mulcair recently: “It’s a clear indication that the Supreme Court had no intention all along of ever dealing with this issue seriously.”

Take another look at those words. Those are the words of a man who aspires to be prime minister — smearing the highest court in the land, suggesting that it is lawless.

That it is engaged in cover-up. As I said at an Ottawa conference this week — as one of Mulcair’s most ardent defenders angrily sat beside me — those comments are beyond the pale. They are disgusting and despicable.

And they disqualify Thomas Mulcair to be prime minister.

Why did Mulcair — Angry Tom, as he is widely known — pursue such a reckless course? Why did he so irresponsibly seek to reopen old wounds and divide Canadians? Because he knows he will never be prime minister.

Because he knows that his current post, leader of the opposition, is the best he can ever hope for. Because he is always prepared to cut a deal with the separatists to advance his career, and to hell with Canada.

There’s been a pattern in Mulcair’s public life. At those points where history is watching, at those moments where he has been called upon to choose Canada or Quebec, he chooses the latter. At every juncture where he could have promoted Canada — with the Sherbrooke Declaration, with the Clarity Act, with the flag — Mulcair declined to do so. He put his partisan interest ahead of the national interest.

At a certain point in a politician’s career, a picture reveals itself. Mulcair’s portrait is one that depicts an angry, bitter old man, one who is literally prepared to put the country at risk to curry favour with separatists. Mulcair is a disgrace. He isn’t fit to be a dog catcher, let alone prime minister of Canada.