Just hours after Stephen Harper announced he was resigning his Calgary Heritage seat, the Liberal Party sent out an email blast to its supporters. Looking for donations, the party said it was hoping to kick-start its efforts to elect a Liberal MP in Harper's vacated riding.

It's an ambitious appeal. The Liberals were beaten in Calgary Heritage last fall by almost 38 percentage points and more than 22,000 votes.

Byelections will need to be held soon in four ridings. The fundraising request from the Liberals mentioned two of them: Harper's and Medicine Hat–Cardston–Warner. That seat was left vacant this spring when Conservative MP Jim Hillyer died of a heart attack. A byelection campaign needs to be called for that riding within a few weeks.

A byelection will also be held in Ottawa–Vanier, but due to the recency of former Liberal MP Mauril Bélanger's death it is possible the government will wait to bundle this vote with one in Jason Kenney's Calgary Midnapore riding. Kenney says he'll resign that seat once the Alberta Progressive Conservative leadership campaign officially begins in October.

That the Liberal fundraising email mentioned only Calgary Heritage and Medicine Hat–Cardston–Warner suggests this could be the government's plan.

Tough ridings for the Liberals

In any case, these three Alberta ridings will be tough nuts for the Liberals to crack. Kenney won Calgary Midnapore in 2015 with 66.7 per cent of the vote, defeating the Liberals' Haley Brown by 44 points. In the former prime minister's riding, the Liberals' Brendan Miles captured just 26 per cent of the vote.

And Medicine Hat–Cardston–Warner is one of the safest Conservative ridings in the country. Hillyer won 68.8 per cent of ballots cast there in October. The Liberals' Glen Allen took just 17.9 per cent, putting him almost 51 points behind.

Results of the 2015 federal election in the Alberta ridings of Calgary Heritage, Calgary Midnapore, and Medicine Hat–Cardston–Warner.

But if the Liberals are serious about mounting a viable campaign for any of these three seats, they could point to some of their recent successes in Alberta byelections.

Though they lost all three contests, in 2014 the Liberals saw a swing away from the Conservatives and toward their candidates in byelections held in Macleod (a 22-point swing compared to the 2011 results), Yellowhead (32 points) and Fort McMurray–Athabasca (50 points).

In 2012, the Liberals nearly won Calgary Centre with a 36-point swing. The party ended up winning the riding in the last federal election.

Replicating the swing the Liberals experienced in Calgary Centre would put Calgary Heritage into play. Replicating the swing in Fort McMurray–Athabasca would put all three ridings in range.

But the current political landscape in the province does not suggest such a swing is in the cards.

Importance of local candidate

The precedent of a byelection forced by the retirement of a defeated prime minister is hard to find. The last time any byelection was held in similar circumstances to the one in Calgary Heritage was in 1939, following the resignation of R.B. Bennett. The winner won by acclamation.

The last time any party overcame a margin at least as large as Calgary Heritage's was in 2010, when the Liberals took Winnipeg North away from the New Democrats after the NDP had won the seat by 40 points in 2008.

A margin as wide as Medicine Hat–Cardston–Warner's was overcome in a byelection nearly 30 years ago, when the New Democrats won the riding of St. John's East away from the Tories. The PCs had won it by 72 points in the preceding election.

In both of these cases, however, the victory could largely be chalked up to the strength of the local candidate. The Liberals had put forward Kevin Lamoureux in Winnipeg North, a long-time provincial Liberal MLA. In St. John's East, the NDP had nominated Jack Harris, a well-known lawyer who would later go on to lead the provincial NDP before returning to federal politics.

The Liberals will likely need to have a local candidate of similar renown if they are to have any chance whatsoever.

Conservatives still lead by wide margin in Alberta

The Conservatives captured 59.6 per cent of the vote in Alberta in last year's federal election. The Liberals took 24.5 per cent.

In recent polls, the Conservatives have averaged 56 per cent support in the province, while the Liberals have averaged 31 per cent.

Results of the 2015 federal election in Alberta vs. the average of polls conducted in Alberta in July and August 2016.

Though that does suggest the Liberals have made some gains at the expense of the Conservatives, the swing between the two parties is just 10 points. That is nowhere near the kind of swing the Liberals would need to put any of the three Alberta ridings in play.

Justin Trudeau's own popularity is limited in Alberta. In two polls, his approval rating has registered between 38 and 43 per cent, with between 49 and 54 per cent of Albertans disapproving of him. Interim Conservative leader Rona Ambrose, who hails from Edmonton, has better numbers than the prime minister.

So for the Liberals to campaign on the premise of being competitive in any of these three Alberta ridings is overly optimistic.

Instead, their benchmark should be scoring about 23 per cent in Medicine Hat–Cardston–Warner and 32 per cent in Calgary Heritage. Numbers like these would serve to back up the national polls and confirm the validity of their post-election popularity.

Doing better than these scores could be chalked up to a strong local campaign. Worse than these might suggest that the Liberals' enduring polling honeymoon is superficial.

Nevertheless, these Alberta byelections — whenever they are held — will pose a test to both the Liberals and the Conservatives. The Liberals have something to prove. The Conservatives have some big shoes to fill.

Stephen Harper and Jason Kenney are arguably the two figures most responsible for making the modern Conservative Party what it is today. Replacing them — and matching their past electoral successes — may be the toughest test of all.