politics is a tricky game Canada 1 
Mr. Trudeau weighed  the costs benefits of his promise and simply folded knowing in 2 months no one will care,  and to go ahead would have been the fight of his life.... for what?
It was never a clear question put to the electorate with clean hands ( ie this is exactly what I propose , it will work like this, if you like it vote for me)  It was a mushball thrown in beside the deficit predictions.
Those supporters who believed him , and genuinely wanted reform , got jobbed on this one,  but his bet , reasonably , is those supporters will forgive and forget and support him next time round.
He's right!