The biggest problem for the old PCs is the Liberals usually swept Quebec thus putting them at a disadvantage, but if you look at English Canada, the PCs beat out the Liberals 60% of the time whereas Harper in both 2004 and 2015 when he showed his true colours couldn't even beat the Liberals there.  Since 1980, the Liberals have not had the lock on Quebec they once had thus creating a greater opportunity and opening which Mulroney took advantage of, but leaders since have not.