Peter MacKay's bid for the Conservative Party leadership officially begins today and he's already starting with a big lead — at least among members of the Conservative caucus.

Endorsements from MPs probably didn't play a decisive role in the party's 2017 leadership race, but they could have made a difference in what turned out to be a close contest. How important could they prove to be this time?

A single tweet from MacKay saying "I'm in" was enough to get a few Conservative MPs to announce their support for the former cabinet minister and last leader of the federal Progressive Conservative Party. As of late Friday, MacKay had received the endorsements of 11 MPs.

They include six MPs from Ontario (Dean Allison, Colin Carrie, Scot Davidson, Ben Lobb, Dave MacKenzie and Doug Shipley), two from British Columbia (Ed Fast and Kerry-Lynne Findlay), two from Alberta (Ziad Aboultaif and Blaine Calkins) and one from Quebec (Pierre Paul-Hus).

MacKay also has received the endorsement of prominent provincial politicians such as Ontario PC cabinet minister Caroline Mulroney and Tim Houston, the leader of the Nova Scotia PC Party.

Now that we know Ontario MP Pierre Poilievre will not be running for the leadership, MacKay's chief competitor appears to be Erin O'Toole, who finished third in the 2017 race and whose own campaign will launch soon. That makes Carrie's endorsement particularly notable, as the Oshawa MP backed O'Toole — who represents the neighbouring riding of Durham — in 2017.

He's one of three MPs who endorsed O'Toole in 2017 and are putting their weight behind MacKay this time.

It's certainly a show of strength from MacKay's campaign, one that gives an impression of momentum right from the start. But just what tangible impacts do endorsements have in leadership races — and what could their impact be in this contest?

Endorsements pulled their weight in 2017

According to the rules of the Conservative leadership contest, every riding in the country is worth 100 points and candidates receive a number of points equal to their share of the vote in each riding.

The 70 MPs who endorsed a leadership contestant in the 2017 race boosted their candidates by an average of 11 points in their ridings, compared to the candidates' performance in ridings in the same provinces where they did not receive endorsements. This phenomenon was pretty widespread — only five Conservative MPs out of the 70 who made endorsements failed to give their candidates a boost in their ridings.

That boost could have made the difference between Andrew Scheer and Maxime Bernier, the top two finishers in 2017. Although these "endorsement boosts" represented only a small share of the 33,800 points up for grabs in Canada's 338 ridings, Scheer's estimated boost was larger than the margin that separated him and Bernier. Had Scheer not gotten the endorsements he did, he might not have won such a close race.

Endorsements are not necessarily predictive, though. Bernier had little support within the Conservative caucus and still led on 12 of 13 ballots. O'Toole boasted the most caucus endorsements, but finished well back of Scheer and Bernier in third place.

Will 2020's race be any different?

Generally, however, candidates who win leadership races in Canada receive a significant number — if not most — of the endorsements from their party's caucus. Why?

It's kind of a chicken-or-egg question. Do MPs endorse the people they believe will win out of self-interest, or do MP endorsements help them win? In the end, the MPs doing the endorsing are likely a mix of bandwagon-jumpers and people willing to put in the actual work to help a candidate win.

Endorsements could make a difference in the 2020 iteration of the Conservative leadership race. For one thing, with 22 more MPs in the Conservative caucus there are now more endorsements up for grabs.

Conservative MP Erin O'Toole will be launching his second leadership bid soon. In 2017, he had more MP endorsements than any other candidate. (Justin Tang / Canadian Press)

The length of the race also might put a premium on Conservative MPs' pre-existing networks in their constituencies. Candidates only have until April 17 to sign up new members who will be eligible to vote in June — that's just 83 days from now. In the last campaign, candidates had just over a year to recruit new members. They more than doubled the size of the membership base in the process.

Unless O'Toole — who had the backing of nearly a third of the caucus in 2017 — can start to build his own roster of endorsements soon, MacKay's advantage might become self-sustaining, discouraging caucus members from backing anyone but the heir apparent.

When all is said and done, no one wants to be the losing side. MacKay is already trying to demonstrate which side that is likely to be.