What tipping point seats say about Liberal, Conservative paths to victory

There's one number that means more than anything in this election campaign for Justin Trudeau and Andrew Scheer: 170. That's the number of seats needed for a majority government and the seats that get them to and past that threshold reveal what their paths to a majority depend on.

Political analysts in the United States often refer to "tipping point" states in presidential elections, referring to the state that is most likely to put a candidate over the threshold required to win the electoral college and so the White House.

In the Canadian context, a tipping point riding would be the one that is the 170th easiest for a party to win.

In 2015, that riding for the Liberals was Ontario's NewmarketAurora, won by Kyle Peterson by a margin of 2.6 percentage points, the 170th widest margin of victory for any Liberal candidate.

It's the kind of riding that is emblematic of why Trudeau's Liberals secured a majority government that year. Located in the suburbs north of Toronto, it had voted for Stephen Harper's Conservatives by a margin of 30 points in the 2011 federal election. The Liberals won in 2015 because they had lured these suburban voters away from the Harper Conservatives.

The 169th and 171st seats for the Liberals, KildonanSt. Paul in suburban Winnipeg and Pitt MeadowsMaple Ridge in B.C.'s Lower Mainland, also fit this mould.

It's impossible to determine with complete certainty what the Liberal and Conservativetipping point ridings might be in 2019, but based on current polling levels and the seat projection model used in the CBC's Poll Tracker we can make some informed guesses.

Liberal tipping points in the Golden Horseshoe

According to the model, the three ridings straddling the 170-seat threshold are all along the shores of Lake Ontario: St. Catharines, Burlington and TorontoDanforth. They speak to the two-front electoral battle the Liberals are waging in this campaign.

These are ridings won by narrow margins in the last election. The Liberals beat the Conservatives by about six percentage points in St. Catharines(which got a visit from Scheer last week) and 3.5 points in Burlington. Voters in both of these seats backed Harper's Conservatives by a margin of 30 points over the Liberals in 2011.

It shows how the path to a re-elected Liberal government still relies on keeping the support of voters in Canada's mid-sized cities and in the suburbs assuming they have the backing of urban voters as well.

That's where TorontoDanforth comes in. The Liberals just squeaked by the New Democrats by a margin of two points in the last election in a riding that the late Jack Layton won by a margin of 43 points in 2011.

The NDP is struggling in the polls, but the party still has a base of support in central Toronto and Trudeau doesn't appear to be taking TorontoDanforth for granted. The Liberal leader stoppedin the riding duringthe second week of the campaign.

If the Liberals can hold off the New Democrats in the urban centres of the country and hold on to the marginal suburban seats they won in 2015, then Trudeau can look forward to be being prime minister for at least another four years.

Conservative tipping points still in the suburbs

The Conservatives have more ground to make up, having fallen 71 seats short of a majority government in the last election. The seats that get them there are located in the suburbs of two of Canada'slargest cities: York Centre and Brampton Centre in the Greater Toronto Area and Burnaby South in Greater Vancouver.

Burnaby South is a complicated case, since NDP Leader Jagmeet Singh is the incumbent. But it can serve as a proxy for the other seats in the Lower Mainland the Conservatives need to win to secure a majority government. The party won two of the neighbouring seats in 2011 and was only four points behind the New Democrats in the current boundaries of Burnaby South that year.

The National's face-to-face interviews

CBC is hosting a series of face-to-face interviews between undecided voters and federal leaders campaigning for next month's election.

How to watch:
Watch the interviews on CBC News Network starting at 8 p.m. ET
Watch on the CBC News App or CBC Gem at 8 p.m. ET
Watch onThe Nationalat 10 p.m. on CBC TV across the country.

York Centre and Brampton Centre, however, are squarely within the Conservatives' sights. Scheer stopped in York Centre, a riding his party won by 15 points in 2011 before losing it to the Liberals by three points in 2015, in the first week of the campaign. Brampton Centre was secured by the Liberals by a more comfortable 15-point margin in the last election, but voters in the riding backed the Conservatives by 21 points in 2011.

For the Conservatives, no majority government is possible without significant gains in the 905 area code that surrounds Toronto, including Brampton's five ridings. But Scheer might also need to infiltrate Toronto itself with seats like York Centre, as Harper did eight years ago.

Watch for trips to more tipping points

Based on current polling, only the Liberals and Conservatives are plausibly in the running to form a majority government. For the New Democrats, they might have to be more worried about a different tipping point 12, the number of seats required to obtain recognized party status in the House of Commons.

It's a threshold that is probably out of reach for the Greens and the People's Party, though the Bloc Qubcois seems well-positioned to win at least that many. The New Democrats are currently projected to clear that bar, but current projections make it look a little too close for comfort. That might become apparent if we see more visits by Singh to a seat like Windsor West, which is a 12-seat tipping point riding for the party.

Over the course of the next three weeks, the landscape could shift and the tipping points with them. The Liberals might be able to afford to lose more seats in the Golden Horseshoe if they make more progress in Quebec. The Conservatives might not need as many GTA ridings if their numbers improve in Atlantic Canada.

But one of the clearest indications of which ridings are going to be the decisive ones in this campaign remains where the leaders decide to spend their precious time. Keep following the leaders voters in the tipping point ridingswill be seeing a lot of them.