Alberta's Progressive Conservatives remain deeply divided over a proposal from leadership candidate Jason Kenney to merge their party with the more socially conservative Wildrose Party.

That division was on full display Sunday as Mr. Kenney took to the stage in Alberta's capital city for a debate between the four candidates running to lead the PC party. The three other candidates in the race reject Mr. Kenney's merger proposal.

"Folks, this is a hostile takeover of our party," warned Stephen Khan, a former provincial cabinet minister running for the leadership. During a bitter exchange, he questioned where Mr. Kenney's support was when the party needed help in past elections. "I was working hard on behalf of the Progressive Conservative Party and you, sir, were supporting the Wildrose.

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"You haven't been a Progressive Conservative until just this summer when you decided to, honestly, try to destroy our party," he said to a mixture of jeers and applause.

Mr. Kenney, a former high-profile cabinet minister who held the immigration and defence portfolios under Prime Minister Stephen Harper, has dominated the race to lead Alberta's Tories. When asked later by reporters, he dismissed Mr. Kahn's suggestion of a hostile takeover as "ridiculous."

After the debate, Mr. Kenney said he felt like a punching bag on the stage, as the other candidates either directly or indirectly attacked his record. He said his campaign will review the format before the next debate. "It didn't seem reasonable to me. I didn't go on this stage with the intention of criticizing any of my colleagues," he said.

The PC party, a political machine that dominated Alberta politics for more than four decades, is searching for an identity after a historic defeat in 2015 that saw it swept from power and reduced to third place. The New Democrats under Rachel Notley won that election.

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"Albertans want their province back," Mr. Kenney argued during the debate. "I am proposing a big, broad, tolerant, diverse, sensible, free-enterprise coalition."

The other candidates dismissed his proposal as unworkable before the next election in 2019.

"Simply duct-taping two broken parties together isn't going to elect small-c conservative MLAs," said Byron Nelson, a Calgary lawyer running for the leadership.

Mr. Khan warned of what could happen under Mr. Kenney's leadership and said he might not keep his party membership if Mr. Kenney wins. "If that should happen, I believe we're going to end up in a U.S. style of politics with a divisive angry party on the right and an ideologically driven party on the left," he said.

The candidates also took aim at Prime Minister Justin Trudeau's comment on Friday that Alberta's oil sands industry will need to be "phased out" as the country transitions to a lower-carbon economy. The suggestion that Alberta's energy industry has no long-term future was met by howls of protest from all four candidates.

Mr. Kenney's campaign has dominated in the leadership race so far, winning most of the local battles for delegates necessary to win the leadership. He's also collected more endorsements than all his opponents combined, and Mr. Harper has appeared alongside him during the campaign.

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While he has won most of the battles to this point, Mr. Kenney's campaign has also tested the limits of the party's code of conduct. His campaign has been fined for ethical lapses, and the results of an Edmonton vote were thrown out after the former minister's campaign broke party rules.

There were also allegations of harassment by Mr. Kenney's campaign after a party convention in Red Deer last November. Former leadership candidate Sandra Jansen said she was the target of sexism and personal attacks. She blamed much of the attacks on Mr. Kenney's supporters.

In the hours before Sunday's debate, Alan Hallman was suspended from the party. A long-time conservative organizer in Alberta, Mr. Hallman was a member of Mr. Kenney's campaign. Party president Katherine O'Neill would not say what Mr. Hallman had done.

"His membership was suspended for a year. He's not allowed at PC events, he's not allowed to access PC data, but I will not go into the details of why," Ms. O'Neill said, adding that it was a unanimous decision of the party's board. "After Red Deer, we were very clear that zero tolerance means zero tolerance. If we were going to be confronted with any type of behaviour that the party deemed unacceptable, we would take action."

Mr. Kenney said that his campaign should not be linked to Mr. Hallman's behaviour and that he had severed his ties to the organizer. "Our campaign has been unremittingly positive. We've maintained a positive tone. One guy did a late-night tweet which was colourful and he thought was humorous. He's apologized for that and he's been held to account," Mr. Kenney said.