With Mulcair freshly installed as the new NDP leader, the battle over which opposition party will emerge as the national alternative to the ruling Conservatives has begun in earnest.
The battle escalated into trash talk Wednesday as a new poll suggested the NDP is enjoying a big bounce in popularity since Mulcair was chosen leader on March 24.
The Canadian Press Harris-Decima survey indicates the New Democrats surged into a statistical tie with the Conservatives, with the parties at 32 and 34 per cent support respectively.
The NDP boost came almost entirely at the expense of the Liberals, who slipped back to 19 per cent — the same all-time low they received in last May's election when the self-styled natural governing party was reduced to a third-party rump.
Rae, the interim Liberal leader, kicked off a round of personal barbs Wednesday, equating Mulcair's combative, ultra-partisan style to that of Prime Minister Stephen Harper. He dubbed the NDP leader "mini-Harper."
Rae pointed to the NDP ploy to monopolize debate on last week's budget as evidence that Mulcair has ditched the respectful, more civilized approach to politics championed by his predecessor, the late Jack Layton.
The first two official Opposition interveners are entitled to unlimited time to speak and NDP finance critic Peter Julian took full advantage of that, speaking for more than 13 hours over three days. Liberals got their first shot at joining the debate — a mere 20 minutes — late Tuesday, once Julian finally wrapped up.
Rae said the ploy accomplished nothing other than prevent some 40 MPs, of various parties, from speaking on the budget.
"If there was any doubt in anyone's mind in Canada, let me just say that the era of love and good feeling is clearly over inside the NDP. It's a new regime."
Invoking Layton's deathbed social democratic manifesto, Rae added: "We've now moved to a world where anger apparently is better than love, arrogance is now better than humility and petulance is much stronger than respect.
Mulcair dismissed Rae's salvo as the product of someone who sees his hopes of becoming the permanent Liberal leader dimming amid the publicity generated by Montreal MP Justin Trudeau's victory last weekend in a charity boxing match.
"I believe that Mr. Rae is quite concerned about the arrival of Mr. Trudeau on the scene and the recent attention being paid to him. So I think he's having a bit of a tough week," he said, apparently oblivious to the fact that Trudeau has ruled out running for his party's leadership.
Mulcair made it clear, as far as he's concerned, the Liberals are irrelevant. He made no apologies for monopolizing the budget debate, maintaining that Liberals have nothing useful to add to the discussion.
"They don't have anything to say about the Conservative budget because, like usual, they agree with the Conservative budget. They agreed with the last five Conservative budgets when they were the official Opposition; they're in agreement with this one," he said, ignoring the fact that Liberals voted against the 2011 budget and are opposed to the latest fiscal blueprint.
Mulcair portrayed the NDP, which vaulted into second place in last May's election for the first time in its 51-year history, as a more rigorous, effective official Opposition than the Liberals ever were.
"But now there's an official Opposition that's going to stand up in front of Stephen Harper, give a real argument as to why things should be done differently ... That's the official Opposition of the NDP. Canadians are relieved that we no longer have the Liberals who roll over at every budget and vote with the Conservatives. They finally do have a party standing up for them."
Mulcair also accused the Liberals of using only 11 of their 20 allotted minutes to debate the budget on Tuesday, proof, he maintained, that they have nothing to say.
"So all that whinging, they got the time and they didn't even use it," he scoffed.
Rae shot back that Mulcair "would not know the truth if he ran into it in bright daylight." In fact, he said Liberals split their time between two MPs and had to cut their interventions slightly short of 20 minutes to ensure the Liberal sub-amendment to the budget made it onto the order paper before the deadline.
As for the notion that NDP was engaged in a filibuster, Rae said: "This was not a filibuster, this was an ego trip and there's a big difference."
He went further later, calling the ploy "an act of arrogance and self-reverence that is unbecoming of a leader of a political party."
Rae and the Liberals had been enjoying somewhat of a comeback over the past few months, while the NDP was focused on its leadership contest. Some polls suggested the two opposition parties were essentially tied, with support in the mid-20s.
The latest poll, however, suggests the NDP is now enjoying a honeymoon with its new leader.
The orange surge was particularly strong in Quebec, Mulcair's home base, where the NDP has vaulted back in front with 39 per cent to the Bloc Quebecois' 24; Liberals and Conservatives were tied at 14 per cent.
The NDP was also leading in British Columbia, with 44 per cent to 30 for the Tories, 13 for the Liberals and 11 for the Greens.
The telephone survey of 2,003 Canadians was conducted March 22-April 2 and is considered accurate within plus or minus 2.2 percentage points, 19 times in 20.
Also on HuffPost