The Liberals lost the by-election because people are tired of Justin Trudeau, and they don't think the Liberal policies will help them.
Nine years is a lot for a Prime Minister to be in office. Nine years in office in the middle of an affordability crisis, is ten times worst.
You have to know when it is your time to go. Let someone like Melanie Joly or Mark Carney take the reins and set their own agenda.
The Liberals best hope is for a new leader to hold the Conservatives to a minority government. For that to happen Justin Trudeau has to go.