Former Conservative Prime Minister Stephen Harper endorsed Pierre Poilievre to be the next party leader.

In a rare public return to party politics, Harper, who did not enter the Conservative leadership races in 2017 and 2020, released a short video on Twitter on Monday discussing his endorsement.

Harper says the race for party leadership is full of candidates, but one stands out.

The former Prime Minister says Poilievre served as a strong minister under his leadership when the Conservatives were last in power, before being defeated by Liberal Prime Minister Justin Trudeau in 2015.

Harper said, referring to Poilievre's advocacy on economic issues like inflation and debt: "In recent years, he has been the party’s strongest critic."

"He proposes answers rooted in sound conservative ideas, but answers that adapt to today’s realities."

Harper's endorsement comes less than two months before the race, as party members are in the process of filling out their ballots by mail.

The race to lead Harper’s former party has been described as a battle for its soul, sometimes including some personal attacks between candidates.

Poilievre has been criticized by former Quebec Premier Jean Charest, who is also a candidate in the leadership race, and others for having ideas and a tone that would make the Conservatives unable to win the next general election after three consecutive defeats.

Harper, in his endorsement video, offered a contrary view. The former Prime Minister says Poilievre not only has the strongest support within the party base of any candidate in the race, but he is popular with current members and brings large numbers of new members.

Harper added: "This is how we win the next federal election." "In my opinion, Pierre has made the strongest case ever that he is the person to do it."

Charest released a statement following Harper's video, describing the endorsement of Poilievre as a "personal choice." Charest’s statement said "The Conservatives only win when we are united.