Former premier Mike Harcourt's disenchantment with the NDP is a sign of the challenge ahead for the party after last year's election loss, leadership candidates John Horgan and Mike Farnworth said Tuesday.

Harcourt has let his party membership lapse and gave several interviews this week to express his disappointment with the NDP's performance in the 2013 election. Harcourt told the he is not sure if his decision to quit the party is "a trial separation or a decree absolute," but he won't be voting in the leadership contest in September.

Horgan said he has spoken with Harcourt in recent weeks about the party's standing in rural B.C., particularly after leader Adrian Dix's mid-campaign decision to oppose the expansion of the Trans-Mountain oil pipeline from northern Alberta to Burnaby.

"The message it sends to me is that I have a lot of work to do," Horgan said. "I have a lot of work to convince Mike Harcourt and other New Democrats and all British Columbians that there's a better way for us to proceed, a balanced approach to the economy and the environment."

Harcourt, the former Vancouver mayor who served as premier from 1991 to 1996, in the 2011 leadership campaign.

Farnworth said Tuesday he agrees with Harcourt's criticism, and the struggle to balance resource development with environmental concern has a long history in the NDP. It was Harcourt who faced the "war in the woods" in the 1990s over coastal logging and came up with land use plans that still serve B.C. today, he said.

"I think Mike is saying what he thought, and it's reflective of the comments we heard after the election last May," Farnworth said.

NDP members vote this fall on their choice to succeed Dix, with results to be revealed Sept. 28.