Conservative Leader Andrew Scheer has taken heat from some of his defeated candidates this week — but those who lost in October aren't the only ones with reasons to want a change at the top.

Most of the Conservative incumbents who won re-election in Ontario and Quebec did so despite a drop in their share of the vote — a drop that risked costing some of them their seats.

Meanwhile, little more than a third of the entire Conservative caucus represent ridings where Conservative members backed Scheer on the first ballot of the 2017 leadership race. An even smaller number of Conservatives from those ridings endorsed Scheer's initial bid for the leadership.

It raises the question of how many Conservative MPs would go to the wall for Scheer if calls for his resignation from within the party continue to grow.

Scheer's Conservatives won 22 more seats in 2019 than the party did in 2015, and a greater share of the popular vote. But that increase was driven primarily by gains in Western Canada, where grievances with the federal government are deep-seated and have been amplified by Premier Jason Kenney in Alberta and Premier Scott Moe in Saskatchewan.

In Ontario and Quebec, however, the party actually lost support and made a net gain of only one seat.

It means that the caucus is split between MPs who increased their own share of the vote in their ridings over 2015 — and those who didn't. And it's a regional split: of the 90 Conservative MPs who took a greater share of the vote than they (or their predecessors) did in the last election, 83 represent seats in British Columbia, Alberta, Saskatchewan and Manitoba.

Of the 31 Conservative MPs who took a smaller share of the vote this time, 28 are in Ontario and Quebec. Those 28 MPs represent 58 per cent of the Conservatives' Ontario caucus and 70 per cent of the Quebec Conservative caucus.

Those MPs do not have Scheer to thank for their re-election. Five of them won by narrow margins of five points or less, suggesting that Scheer's election performance may have come close to costing them their seats.

Many of the MPs who experienced the biggest jump in support represent bedrock Conservative ridings in Alberta and Saskatchewan — seats that almost certainly will keep voting Conservative regardless of who the leader is.

It all suggests that Scheer won't be able to rely solely on the political self-interest of caucus to keep Conservative MPs solidly behind him.

Most of today's caucus did not back Scheer in 2017

Scheer's victory in the 2017 leadership race was a close-run thing. It took 13 ballots for Scheer to defeat Maxime Bernier by the narrowest of margins.

Scheer was not the first choice of party members (he finished behind Bernier on every ballot but the last). He also was not the first choice of caucus; most MP endorsements went to other contestants.

Out of today's Conservative caucus of 121 MPs elected in October, just 21 endorsed Scheer during the leadership contest. That puts Scheer behind Ontario MP Erin O'Toole, the third-place finisher in that race; 28 MPs now in caucus backed O'Toole in 2017.

Andrew Scheer, right, is congratulated by Maxime Bernier after being elected the new leader of the federal Conservative Party in Toronto on May 27, 2017. (Frank Gunn/Canadian Press)

Another 13 sitting MPs endorsed other contestants — Bernier, Kellie Leitch, Lisa Raitt and Michael Chong. Of those four candidates, only Chong is still in the Conservative caucus. About half of the current caucus members did not endorse a candidate.

Scheer was not the first choice of party members in the 121 ridings now represented by Conservative MPs. On average, he got 27 per cent of the vote in these ridings on the first ballot of the leadership race and finished ahead of all other candidates in just 44 of them.

Of the 121 seats represented by Conservatives, Bernier (now the leader of the People's Party) placed first in 58. O'Toole finished first in 10, socially conservative contestants Pierre Lemieux and Brad Trost placed first in a combined seven ridings and Leitch and Chong finished first in their own ridings.

On the final leadership ballot, Scheer averaged 56 per cent of the vote in these 121 seats — a better result than he got in the ridings that did not elect a Conservative MP in October — and won 82 of them, with Bernier taking the other 39.

Ontario MPs Michael Chong and Erin O'Toole and Conservative Leader Andrew Scheer, left to right, are three of the four contestants from the 2017 Conservative leadership race still in caucus. Quebec MP Steven Blaney is the other. (Andrew Vaughan/Canadian Press)

In all, only 64 of 121 current Conservative MPs represent ridings where the party increased its share of the vote in the last election and where party members supported Scheer on the final ballot of the 2017 leadership race.

That's not a particularly deep foundation of support for a beleaguered leader.

So far, no Conservative MP has publicly broken ranks and called for Scheer's resignation. But Scheer did fire two top staffers last week. Sources told CBC News that some members of caucus presented him with a list of people he needed to remove from his office in the aftermath of the election defeat — an indication that MPs are flexing some muscle.

If caucus does stay behind Scheer through to the mandatory leadership review vote in April, these numbers suggest it won't be because Conservative MPs feel they have him to thank for their seats in Parliament.

Instead, it might be Scheer who has his caucus to thank for not swiftly pushing him out — letting party members (or Scheer himself) ultimately decide his fate.