Early on in How We Lead, Joe Clark extends an anecdote from his time as prime minister into a critique of the Harper government.

Clark recalls a conversation with his Zambian counterpart, Kenneth Kaunda, at a 1979 Commonwealth meeting. Kaunda was surprised, Clark writes. He didn't expect the new Progressive Conservative prime minister to take many of the same positions as his predecessor, Pierre Trudeau.

But Clark had a simple answer: "We represent the same country."

That, Clark writes, had long been the norm of governments elected to Ottawa. A norm that ended with the election of Stephen Harper in 2006 and introduction of policy changes he says have had ironic and negative consequences on a key Canadian sector: the oilsands.

Speaking with iPolitics, Clark said the break in continuity is hard to miss on the environmental file. From its withdrawal from the Kyoto Protocol to dumping the UN Convention to Combat Desertification, the Harper government has taken a divisive approach to international climate discussions. But the government that has seen Canada become a perennial favourite for the tongue-in-cheek Fossil Award may have also made selling Canadian crude abroad more difficult, Clark contends.

"I think the position Canada took on environmental issues -- really since this government came into office -- has made it more difficult to get approval on Keystone," he said.

"I don't pretend to understand all of the dynamics the president is dealing with, but clearly some of the people on his mind will be people who would be alarmed at the change in the Canadian position on environmental matters."

In the book, Clark singles out the Montreal conference that led to the ban on ozone-depleting chlorofluorocarbons (CFCs) and the 1991 acid-rain treaty as initiatives that helped develop Canada's reputation as environmental leader.

"I think the president would've been less skeptical about the government's plans if the Mulroney-Chrétien policy on the environment had been maintained," he told iPolitics.

Having created an adversarial relationship with environmental groups, though, Clark believes that reputation may be hard to re-establish -- though he adds the government is trying.

"The problem in this case is that the federal government has developed an image on environmental issues that it's trying to change. In some cases, it's the very ministers who created that image (who) are now trying to change it. And there's a credibility issue there," he said.

It's not just environmental co-operation that's faltered, though.

Generally speaking, Clark argues Canada's relationship with the U.S. has narrowed since a time when the government found common cause on such a wide range of issues that it could disagree on others while maintaining a "deep friendship" that was the envy of the world.

In How We Lead he reminds readers that it was only weeks after Brian Mulroney informed then-president Ronald Reagan Canada wouldn't be participating in the "Star Wars" Strategic Defense Initiative that the White House accepted Canada's invitation to begin free trade negotiations.

"It wasn't simply that we were in the same ballpark. It was that on critical issues, we were on the same team," Clark said.

"There's been a difference in the closeness and enthusiasm of the relationship from the Mulroney era. Obviously the Harper government is not the only subsequent government that faces that deficit. It was a high standard to reach."

BJ Siekierski reports for iPolitics, where this article first appeared.