The socialist wing of the NDP should probably send Justin Trudeau a note of thanks.

If Trudeau and the Liberals hadn't trounced the NDP in 2015, and if they hadn't done so while running on an aggressively progressive platform, the New Democrats would surely not have released the sort of platform they did on Sunday — a platform that practically boasts of the billions in new revenue an NDP government would raise.

Thomas Mulcair's NDP was not entirely opposed to raising taxes. As set out in the party's 2015 platform, a Mulcair government would have increased the corporate tax rate by two points, from 15 to 17 per cent. That NDP also promised to close the tax loophole on stock options — an issue the Trudeau government partially addressed earlier this year.

But the former NDP leader scoffed at raising taxes on the wealthiest Canadians, as Trudeau eventually did. "Several provinces are now at the 50 per cent rate," Mulcair said in 2013. "Beyond that, you're not talking taxation; you're talking confiscation. And that is never going to be part of my policies, going after more individual taxes. Period. Full stop."

Mulcair worried that any increase in personal taxes would tarnish his party's brand. But not raising taxes was also linked with a refusal to run a deficit. Tom Mulcair prided himself on being a serious and experienced "public administrator," and serious public administrators didn't do such things.

Thomas Mulcair previously worried that any increase in personal taxes would tarnish the NDP's brand. (Paul Chiasson/The Canadian Press)

Jagmeet Singh's NDP is apparently not encumbered by such pretence.

As laid out on Sunday, a Singh government would increase the top personal income rate from 33 to 35 per cent; make 75 per cent of capital gains eligible for taxation, up from the current 50 per cent; and introduce a new one per cent "wealth tax" on those with incomes over $20 million.

An NDP government would also increase the corporate tax rate to 18 per cent, it would introduce a 15 per cent foreign buyer's tax on real estate purchases and would apply to GST to foreign-based Internet services, like Netflix.

Then and now

Somewhere Tom Mulcair is feeling faint.

Those tax increases are necessary because of everything else the NDP is promising to do.

In 2015, the NDP promised to work toward universal pharmacare. Singh's NDP is promising to have a national pharmacare system up and running by 2020, and to then add dental care and seniors care to the Canada Health Act, while also funding eye, hearing and mental health care.

In 2015, the NDP promised to build 10,000 new affordable housing units. Singh's NDP is vowing to build 500,000 spaces over 10 years.

In 2019, there are also aspirational goals of free post-secondary education and free public transit. And a Singh government would fund a basic income pilot project, while also increasing funding for child care by $1 billion per year.

There are promises of nearly a dozen national strategies, covering everything from aerospace to freshwater to food waste.

Learn more about the NDP's recently unveiled platform:

NDP Leader Jagmeet Singh was in Hamilton, Ont., to announce his election platform 4 months before the federal election. The leader started by making a promise to expand healthcare in Canada. 2:11

But the boldness isn't limited to new social programs: Singh's NDP would decriminalize all drugs, and they'd lower the voting age to 16.

As for balancing the budget, the NDP isn't particularly worried about it.

"Our fiscal approach ensures that Canada's debt-to-GDP ratio falls over our 10-year fiscal horizon," the party explains, giving itself significant leeway to increase the federal deficit in the short term.

Times, of course, have changed.

In 2015, the NDP was the Official Opposition and competitive in the national polls. Going into that year's campaign, it even held a small lead over both the Conservatives and Liberals. The greatest risk might have seemed to be that the party would scare off potential voters — that the increasingly real prospect of an NDP government would cause swing voters to have second thoughts.

So the NDP struck a reassuring tone, while promoting Mulcair as a more serious, experienced leader than Trudeau.

Four years later, the NDP have neither the political nor the policy room to play it safe.

Fighting weak polling numbers

While surely not to the satisfaction of all progressive activists, the Trudeau government has, in several ways, acted as a moderate NDP government might. And the real NDP has fallen back to a distant third in national polls. After the historic breakthrough of his election as NDP leader, Singh has largely failed to generate any significant excitement.

The NDP currently sits at 15 per cent and is facing the potential for significant losses in the fall election. Fundraising returns are weak. And worse, Elizabeth May's Greens are suddenly not far behind.

The clearest available path back to relevance involves being interesting — with an eye to voters who might wish the Liberals had done more on various fronts and with a mind to ensuring those progressive voters don't move to the Greens.

For certain segments of the NDP's membership, this is no doubt preferable to the 2015 approach. And for certain segments of the public, this might seem like an exciting break from the status quo.

The risk for the NDP in being more interesting is that the party may seem less credible. The Liberals have already begun to needle the New Democrats for having great ideas, but no real plan to make any of it happen.

What the NDP platform lacked on Sunday was anything that looked like a full costing. That is apparently in the works, with plans to submit proposals to the Office of the Parliamentary Budget Officer for an independent review.

Even if the PBO finds that the party's numbers add up, those numbers will surely be big. And big numbers are often hard to carry around.

But whether borne out of circumstance or ideological inclination, this is what the NDP needs to be right now.