Rex Murphy says he understands why Justin Trudeau didn't announce his bid for the Liberal leadership, because once he does there's no turning back.

Read a transcript of this Rex Murphy episode

That’s Justin Trudeau announcing yesterday he didn’t have anything to announce yesterday – but that he might announce something later. The right to announce that you have nothing to announce but that you might announce something later is something only the higher gods in the celebrity firmament can claim. Outside of the teenybopper balladeer Mr. Bieber, Mr. Trudeau is the only other Canadian Justin who can claim it.

Naturally too, the non-announcement announcement was in effect an announcement that in 6 days he will tell the world what it already knows – that he’s running.

Well, it’s a really good thing for the Liberal party that Justin Trudeau is going to run to lead it. Because if he had said ‘no’ – the Liberals would have to call in CSI and commission the autopsy report. It might stagger on a while, be a ghost presence on Twitter, an occasional footnote on an obscure blog, but it’d be over.

If its most famous and popular figure, himself the son of a great Liberal Prime Minister, actually declined to try and save it at its worst– why then it would join the ranks of that so famous Python parrot --- it would be gone, it would be gone again and gone.

From Mr. Trudeau’s perspective, this dynamic cuts both ways. Like his party he didn’t have much choice. He wouldn’t want to be seen as abandoning the party to which his father gave such glory. And, today, half of his own fame, and even more of his political standing is tethered to the idea he was heading to extend the Trudeau drama --- that he was offering a celebrity-sequel to his famous father’s tenure.

So it’s kind of neat: the Liberal party absolutely needed him, and he – not so much but to a degree – needed it. His fame needs fuel, a static story doesn’t sell.

Now – can he win? If he does not win the Liberal leadership we shall have to fire all the astrologers, all the pollsters and pundits, in fact we may have to retire the whole grand science of political speculation – a prospect too dire to contemplate.

Even that’s just a threshold accomplishment. Winning the Liberal leadership is not what it used to be. It is not to be assumed that Justin Trudeau at the head of the Liberal party is at all a match – not for Stephen Harper – but for the new gunslinger in town, Tom Mulcair. Mr. Trudeau’s first challenge, and maybe the tougher one, is Mr. Mulcair. Mr. Mulcair has every reason to see the Liberals stay weak and wounded – and to hold on to the great new NDP base the Liberals once owned.

I can see why he non-announced his bid yesterday … Once really in, there’s no turning back - this is his Rubicon, and will tell us whether the celebrity he so vastly enjoys can be matched by the accomplishments needed to justify it.

For The National, I’m Rex Murphy.