Harper has reason to be scared.
So, what are the risks and rewards of a Trudeau dynasty for the Liberal party, for the ruling Conservatives and for the New Democrats?
For the Liberals, near-term, their leadership-selection process falls into disarray, as candidates flee the juggernaut. Few will want to throw a $75,000 admission fee away. More to the point, what donor will want to invest in a doomed campaign? There may be Grits of the Bay Street variety who decide, for the good of the party, that it cannot be a coronation, and that stalwarts such as Marc Garneau and Denis Coderre must therefore have a shot. But that's a tough sell knowing you're backing, at best, a future industry or environment minister.
But mid-term, whatever the texture of the race, Trudeau will give his party a new lease on life, even if he does little more than needle Prime Minister Stephen Harper and smile for the cameras. That's partly because Harper is now personally vulnerable. Half the population actively dislikes him. And politics is still, at root, a popularity contest.
Near-term for the ruling Conservatives, there's happy news: NDP Leader Tom Mulcair has a rival in Quebec, which will blunt the opposition leader's advance. It's divide-and-conquer: Let Trudeau attack Mulcair, and vice versa, over ground Harper no longer really needs anyhow. He has just five seats in Quebec, making the province irrelevant to his majority.
But mid-term, Harper's team has reason to fear Trudeau's charm, his particular appeal in Quebec, Ontario and B.C., and the Liberal party's time-tested ability to morph into whatever policy shape best suits its needs at any given time. Where Trudeau is strongest - likability - Harper is weakest. In year seven headed for 10, time is not on the prime minister's side in this regard. With Trudeau as his foil, it will be less easy for the PM to cast himself as the dour national bean counter, too busy with his spreadsheets to bother being human.
The PM's forays at the piano, the blue sweater, the hockey book, are fading in the public consciousness. Whether he wants to or not - clearly he resists this kind of pandering, because we haven't seen it recently even when it obviously would have helped him - he will feel pressure to retrieve Soft Harper from the crypt.
For the New Democrats, it's all bad news, near and mid-term. Trudeau's perfect fluency in French, his flair for the dramatic and the boxing match all make him a force to be reckoned with in Quebec, which historically prefers leaders with dash. Trudeau will set out first and foremost to eat the NDP's lunch. There is no reason to believe he won't meet with some success.
The wild card, of course, is Trudeau himself. If he fails to excite with some good ideas, once the initial flurry of interest abates, or if he goes supernova through some asyet unforeseen mistake - always possible for a first-time leadership candidate, but even more of a factor for the untested, the young, and those blessed or cursed with a risktaking gene - then he brings the Liberal party down around his ears and we're in a twoparty system for the foreseeable future.
Sounds like the NDP have more reasons to be scared.