The Conservatives underestimated turnout in October's federal vote, missing the emergence of a bloc of voters that cemented both the Liberals' election-winning hold on Ontario and Quebec and their rejection in Alberta and Saskatchewan, said Conservative campaign manager Hamish Marshall.

The preliminary estimates by Elections Canada put turnout in the federal election at 18.2 million or about 66 per cent of eligible voters, just short of the 68.3 per cent turnout achieved in 2015 — which was the highest level of voter participation in over 20 years.

"Over the course of the campaign, we kept on revising our turnout expectations upward," Marshall told CBC News on Monday. "When it started, we expected turnout to be around 63 or 64 per cent."

The first indication that turnout could beat expectations came in the advance polls, when Elections Canada estimated that participation had jumped by 29 per cent compared to the previous election. Marshall said that he increased his estimate to 65 per cent at that point.

In theory, it would not have taken much to flip the outcome of the election. The Liberals emerged with 157 seats, 36 more than the Conservatives, despite receiving nearly 220,000 fewer votes.

About six million Canadians voted for the Liberals. An analysis of the ridings the party won with the narrowest margins suggests that just 21,446 voters deciding to stay home in these hotly contested districts could have allowed the Conservatives to edge out the Liberals in the final seat count.

Liberals closed the enthusiasm gap

Marshall said that after the advance polling closed a week before election day, he still believed that his party had an advantage over the Liberals in voter enthusiasm.

"We felt that the advance polls had gone well for us and enthusiasm was on our side at that point in the campaign," he said. "Our polling showed that Conservative voters were significantly more likely to say that they were absolutely certain to vote in the election. There was an enthusiasm gap to our advantage."

Public polling at the time also gave the enthusiasm advantage to the Conservatives, although the size of that advantage differed depending on the poll. At the beginning of the campaign, Ipsos found that 77 per cent of Conservative voters said they were "absolutely certain" they'd cast a ballot for that party, compared to 72 per cent of Liberal voters.

By the end of the campaign, that advantage had narrowed only slightly — to 80 per cent among Conservatives and 76 per cent for the Liberals. But Marshall's polling captured a bigger shift.

"Our last round of polling before the final weekend showed that the Liberals had tied us on 'absolutely certain to vote' and that the enthusiasm gap, particularly in Ontario, had vanished," he said.

Public polls also picked up this shift in opinion in Ontario. According to the CBC's Poll Tracker, an aggregation of all publicly available polls, the Liberals held a lead of only four percentage points over the Conservatives in the province a week out from election day.

The day before the vote, the Poll Tracker's estimate put that gap at seven points. In the end, the Liberals won the vote in Ontario by a margin of just over eight points.

Half-a-million unexpected voters

"On election day, turnout blew everyone's expectations out of the water," said Marshall, adding that turnout was about 550,000 greater than his own estimate.

Marshall said that about 220,000 of those 550,000 unexpected voters were living in Alberta and Saskatchewan. "They broke Conservative," he said. "This is one of the reasons we out-polled every pollsters' final prediction for us."

Turnout in those two provinces was among the highest in the country — and the polls did miss the final result for the Conservatives in the Prairies more than they did anywhere else in Canada.

On average, pollsters' final tallies underestimated Conservative support by only one or two points in central and eastern Canada. But in Saskatchewan and Manitoba, the pollsters under-shot the Conservatives by an average of seven points. In Alberta, pollsters underestimated Conservative support by 10 points — enough of a miss to give the party its national popular vote win.

Marshall said that another 100,000 unexpected voters turned out in Quebec, boosting the Liberals past the Bloc Québécois in a number of seats. In fact, the Liberals won six seats in Quebec by a margin of less than 1,000 votes. In all six of those seats, the Bloc finished either second or a very close third.

"About 200,000 in Ontario also broke Liberal," said Marshall, "defeating Conservatives in a dozen close races.

"I think in Ontario the Liberals successfully used the prospect of a Conservative government as a way of motivating disappointed or disaffected Liberals to come out to vote."

By election day, Marshall said, he knew that his party wasn't going to be forming a government.

"I could see who was voting from the reports of our scrutineers across the country," he said. "And while our voters and the Liberal base were coming out at a good rate, as expected, in Ontario we could see that voters identified as undecideds were turning out at the same rate as the Liberal base.

"This was a bad sign, because if they tell our canvassers they are undecided, it's often a way of politely saying, 'I'm not voting for you' or 'I won't bother to vote at all.' There is no doubt we got some of that vote, but that overwhelmingly it was going to our opponents."