Kellie Leitch is falling back and Kevin O'Leary is moving forward in their bids to lead the Conservative Party, according to the latest update to the Conservative Leadership Index.

Fellow contenders Andrew Scheer and Erin O'Toole also improved their standings in the index thanks to some key political endorsements.

The index is a composite of four leadership race metrics (endorsements, contributors, fundraising and polls) that has been developed to help gauge the state of the 14-candidate race to replace Stephen Harper as the party's permanent leader. A full explanation of how the index works can be found here.

Maxime Bernier still tops the index with a score of 20.1 points (suggesting he would capture 20.1 per cent of the vote on the first ballot if that vote were held today), down slightly from where he stood on Mar. 9. O'Leary is next with 18.5 points, up 0.7 points, followed by Scheer at 13.3 points.

O'Toole, inching up to 9.9 points, has moved into fourth place. He displaced Leitch, who dropped 0.7 points to 9.5.

Lisa Raitt and Michael Chong round out the top seven with 6.4 and 5.6 points, respectively. A full breakdown of the index can be found at the bottom of this article.

Deltell endorsement boosts O'Toole

The highest profile endorsement over the past two weeks came from Gérard Deltell, a Quebec Conservative MP and last leader of the provincial Action Démocratique du Québec before it merged with the opposition Coalition Avenir Québec. Deltell threw his weight behind O'Toole, putting the Ontario MP on the map in Quebec.

The value of Deltell's backing has boosted O'Toole to 10 per cent of the endorsement points available in the province (the index awards points according to an endorser's status — see methodology for details).

Conservative leadership contender Erin O'Toole has won the endorsement of Quebec MP Gérard Deltell. (CBC)

O'Toole still ranks behind Scheer in endorsements nationwide, however. The Saskatchewan MP bolstered his Ontario support with four endorsements from the province, including three former MPs and a sitting MPP.

These four Ontario endorsements moved Scheer from fourth to second in the province with an 18 per cent share of Ontario's endorsement points, behind O'Toole's 24 per cent share.

The other candidates in the race lost endorsement point share as O'Toole and Scheer added to their tallies.

Leitch slips in polling score

The index uses a rolling monthly average of polls of Conservative supporters or members. The only surveys conducted over the last month have been by Mainstreet Research for iPolitics. The polling firm interviewed Canadians who have previously donated to the federal Conservatives (or some of their provincial equivalents) and who say they are eligible to cast a ballot in the May 27 leadership vote.

Those sampled would not include new members who are interacting with the party for the first time or those who had donated less than $200 in any one year to the Conservatives in the past.

Leitch's polling score in the index has dropped by 3.1 points to 11.3 per cent. Though she managed 19 per cent support among decided respondents in the most recent Mainstreet/iPolitics survey, that was a sharp departure from the eight to 10 per cent she was registering among decided respondents in polls done in the three weeks prior.

Her score in the rolling average dropped because she had previously been polling as high as 24 per cent among decided respondents — well above Mainstreet's latest result.

O'Leary, Scheer and Raitt take advantage

There have been a few beneficiaries to Leitch's slip in the polling average over the past four weeks.

Ontario MP Raitt has been scoring around nine per cent among decided respondents in Mainstreet's polling, compared to her previous scores of four to seven per cent.

Conservative leadership candidate Kevin O'Leary is still leading in the polls. (Lars Hagberg/Canadian Press)

Scheer has been polling between nine and 12 per cent among decided respondents in recent weeks, compared to his five to seven per cent rating in Mainstreet's first waves of polling in January and early February.

O'Leary still holds an overall lead in the polls, managing between 25 and 29 per cent support, up a little from where he was when he started his campaign in January.

Bernier slipped in Mainstreet's latest sounding, conducted in the midst of O'Leary's allegations about irregularities with membership sign-ups. Prior to that, he was scoring between 22 and 23 per cent.

O'Toole's endorsement strength has yet to show up in the polls. He is still scoring between just three and 5.5 per cent among decided respondents, ranking him behind Leitch, Raitt and Chong.

The other candidates in the race are Steven Blaney, Brad Trost, Pierre Lemieux, Chris Alexander, Andrew Saxton, Deepak Obhrai and Rick Peterson.

The index is based on four different metrics: endorsements, fundraising, contributors and polls. In tests on 14 recent federal and provincial leadership races in which all party members could vote, the index has replicated the first ballot results with a median error of +/- 2.2 points per candidate.

A more detailed explanation of the index's methodology can be found here.

*As Kevin O'Leary entered the race after the end of the last fundraising reporting period, the index substitutes his poll support in place of his fundraising and contributors. Each candidate's average is then adjusted so that the index adds up to 100.