It is still 2.5 years away and while I agree a steep hill to climb not an insurmountable margin.  Lets remember the Liberals were 20 points ahead a year ago, while 4 months ago only 5 points ahead so polls fluctuate.  In Nova Scotia which is having an election on Tuesday, the Liberals 6 months ago were 30 points ahead of the PCs while now only 5-7 points and across the pond the Tories began the campaign at 20 points ahead but are now only 10 points.  So yes I think the Liberals will win in 2019, but I've seen many parties further back in the polls pull off wins like BC Liberals in 2013 (started 20 points behind) or NDP in Alberta who started at 17% in the polls.  Also prior to Trudeau becoming Liberal leader, the Liberals were in the teens and third place so a lot can happen albeit you are right odds favour the Liberals, but no guarantee.