They've pounced on the newly minted NDP leader's musings about the economic impact of Alberta's oilsands to paint him as a divisive, ill-informed, irresponsible enemy of western Canada who is unfit to govern.
But Mulcair isn't backing down. And he's fighting back.
He says the Tories are shirking their duty to protect the environment, allowing oil companies to pursue "unbridled" development and treat Canada as an "unlimited free dumping ground."
The third-party Liberals, meanwhile, are hoping to take advantage of the pitched, polarized battle to position themselves as the "voice of reason."
New Democrats had expected the Tories to go after Mulcair immediately after he was elected leader in late March, in much the same way they demolished the last two Liberal leaders, Stephane Dion and Michael Ignatieff, before they had time to make their own impression on voters.
Until now, however, the Tory attacks have been tepid, at best.
But the gloves finally came off Thursday as Conservatives trained sustained, heavy fire on Mulcair's assertion that booming energy exports, particularly from the oilsands, have created an artificially high dollar that has, in turn, hollowed out Canada's manufacturing sector — a phenomenon dubbed the "Dutch disease."
Canadian Heritage Minister James Moore, who represents a British Columbia riding, led the charge, backed up by a chorus of Tory backbenchers. Moore turned questions from the NDP leader on an unrelated matter into repeat attacks on Mulcair's fitness to be official Opposition leader, much less a future prime minister.
"I am wondering when the leader of the Opposition will apologize to western Canadians for suggesting the strength of the western Canadian economy is a disease on Canada," Moore told the House of Commons.
"He attacks western Canada, he attacks our energy industry, he attacks all of the West and the great work that is being done by western Canadians to contribute to Canada's national unity. He should be ashamed of himself," he thundered.
Moore warmed to his theme with each non-answer to Mulcair's questions.
"He should be ashamed of himself for attacking the West, dividing our country and not even having visited the places (the oilsands) he is attacking. It is unconscionable for someone who wants to be the prime minister of the country to be so utterly irresponsible."
If Mulcair was to actually visit the "the people whose economy he says is a disease in this country," Moore said he might at least "start the pathway back to a little dignity for the leader of the Opposition."
But Mulcair gave as good as he got. He countered that the root cause of the artificially high dollar is the federal government's refusal to enforce its own environmental protection legislation and make energy companies pay the costs of their own pollution.
"We are allowing these companies to use the air, the soil and the water as an unlimited free dumping ground," he said, accusing the Conservatives of using Nigeria, rather than the more progressive Norway, as their model for development.
"Their priority is the unbridled development of the oilsands. We stand for sustainable development in this country."
Mulcair later said the Tories had better think again if they think they can roll over him the way they did Dion and Ignatieff.
"As you can see as usual, when there is a substantive debate, all they can do is scream and try to bully you down. They've picked the wrong guy if they think they're going to bully me."
Interim Liberal leader Bob Rae expressed hope the fireworks may give Liberals a chance to do what they do best: come up the middle between polarized extremes.
"Well, I hope so. I mean I certainly like to be the voice of reason in all this," Rae told reporters.
Rae said Mulcair's "abstract economic theory" that resource development is to blame for the high dollar is "absurd" and questioned his political smarts in sticking to it so vigorously.
"When you're deep in a hole like Mr. Mulcair is, the first thing you do is stop digging. Instead of which, he just kept on digging deeper and deeper."
Rae suggested the oilsands issue has demonstrated that Mulcair does not have "a really deep appreciation of how sensitive these issues are in the national debate" or how proud westerners are that their energy-producing provinces are now the main drivers of Canada's economy.
"We do not gain anything as a country, in my view, from gainsaying their achievements. What we have to do is make sure they're sustainable. That's the key thing."
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