In a speech Wednesday to an NDP caucus retreat, Mulcair didn't mention Justin Trudeau directly.
But the subtext was clear: don't be fooled into thinking that the shiny new Liberal leader heralds a different way of doing politics.
He asserted that Canadians have only one option — the NDP — if they want to put an end to "politics as usual."
Asked later why he refused to mention Trudeau's name, Mulcair was scathing.
"You'd have to point to something that Justin Trudeau's ever done, for me to be able to mention him," he scoffed.
In contrast to Trudeau, who has said "he won't have much to say between now and the next election" on economic policy, Mulcair said the NDP "is talking straight up about serious, concrete things."
He then proceeded to underline his point by reiterating some key NDP economic policies, promising to roll back corporate tax reductions to bring the tax rate more in line with that in the United States and to scrap the Conservative plan to hike the age of eligibility for Old Age Security to 67.
And he ruled out increasing any personal income taxes, including imposing a tax on the wealthiest Canadians in a bid to shrink the increasing income gap between rich and poor.
"It is our intention to increase corporate taxes but I'm categorical we will not increase individual taxes. ... I'm categorical on that: no increases in personal taxes under our administration."
Mulcair promised to unveil more NDP policies "well in advance of the next election," with costing verified by experts. A pan-Canadian energy strategy will be released this fall, he added.
Liberals have vaulted into the lead in most polls since Trudeau took the helm in April, relegating the NDP to its traditional third-place slot.
After barely acknowledging his existence for five months, Mulcair has recently gone on the offensive against Trudeau, evidently concluding that he can no longer wait for the Liberal leader's extended honeymoon to peter out on its own.
Liberal House leader Dominic LeBlanc said Mulcair is sounding desperate.
"It's phoney and desperate to claim that it's somehow a crisis because the 2015 Liberal platform isn't online two years in advance," LeBlanc said in an interview, noting that the NDP platform has not been released either.
Trudeau has offered some detailed policy already — including immediately denouncing Quebec's proposed charter of values while Mulcair was initially "in hiding" — and will do more in the run-up to the election, he added.
LeBlanc predicted Mulcair's attacks will backfire because Canadians want their political leaders to be "hopeful and positive" like Trudeau, not "negative and brooding" like the NDP leader.
Labour Minister Kellie Leitch, meanwhile, jumped on Mulcair's tax plans, including his advocacy of a carbon tax, to assert that "his plan to raise taxes, attack our resource economy and oppose trade will undermine our prosperity and hurt families well into the future."
In his speech Wednesday, Mulcair repeatedly accused the Liberals of being no better or different from the Conservatives on a host of fronts: Senate corruption, income inequality, climate change, protecting their entitlements and their corporate friends.
He referred to the two parties as "old-line parties of the past."
Mulcair seemed particularly intent on casting doubt on Trudeau's stated priority to improve the lot of struggling middle-class families.
Over the last 35 years, Mulcair said, the wealthiest Canadians have seen their incomes grow while the average Canadian family's income has fallen by seven per cent.
"Now, the Liberals may hope that Canadians forget their record, they may hope that enough time has passed," Mulcair said.
"But over those same 35 years, 94 per cent of the income inequality that we've experienced in Canada has happened under Liberal governments, not Conservative. You heard that right — 94 per cent."
He accused both Liberals and Conservatives of having "idly watched a generation of good, full-time jobs disappear."
On the Senate expenses scandal, Mulcair said the issue isn't just about individual senators claiming living and travel expenses to which they weren't entitled.
"It's about the revolving red and blue doors of Liberal and Conservative entitlement and corruption," he said.
"The fact is, Ottawa is broken. And while the Liberals simply wait for their turn at the trough, the NDP is still the only party that will fix it."
The NDP has long called for abolition of the Senate.
"While the old parties fight to protect their entitlements and their well-connected friends, Canadian families are struggling like never before," he said.
Mulcair further accused Conservatives, "just like the Liberals before them," of gutting rules meant to protect the public, allowing industry to regulate itself in sensitive matters such as food safety, the environment and rail transport.
And he said neither party has done anything to tackle the threat of climate change.
"New Democrats know it's time to chart a different course. And unlike the old-line parties of the past, we're actually going to deliver," he said.