Stephane Dion has left the federal cabinet and quit politics. It obviously wasn’t a voluntary departure, but he managed to give a gracious enough statement. He obviously still wants to be a public servant, and in public life. Where that will be remains to be seen — word is that he was offered some sort of ambassadorship, but is taking time to stew think it over.

His departure was inevitable. As Paul Wells reminds us, the antagonism between Dion and Trudeau goes back aways. He wasn’t a very good foreign affairs minister, and his attempt to formulate some sort of Weberian doctrine to justify the shit-eating that goes along with the job was pathetic.

And before that, Dion was the Liberal leader who led the party to its worst showing since 1867, until whatshisname who replaced him did even worse.

But before that, he was Stephane Dion, the scourge of Quebec sovereigntists, the architect of the Clarity Act, the federalist Sun Tzu who showed Ottawa how to take the fight to the separatists.

That might sound overheated, but it is really hard to overstate how important Dion was to my generation of federalists. We grew up under Mulroney’s Meech and Charlottetown gambits, the fracturing of the PCs, the rise of the Bloc and the heartstopper of 1995. Throughout that entire time, you could fire a cannonball through the House of Commons in the middle of Question Period and run zero risk of hitting anyone who could defend Ottawa’s right to exist on anything other than the most pragmatic of grounds.

The operating assumption of the day, in federalist circles, was that separatists had the arguments, while federalists had sentiment and emotion. It was Dion who taught us that everyone had it exactly backwards: it was the federalists who had all the good arguments, while the separatists were the ones making emotional appeals.

That’s the argument, more or less, of my piece on Dion in tomorrow’s National Post.