Once again, a weakened Liberal government offers the NDP an opening

Defending his decision to have Parliament prorogued until Sept. 23, Justin Trudeau acknowledged the obvious on Monday — his Liberals do not occupy a majority of the seats in the House of Commons.

"As we take a new direction, I think it is extremely important in a democracy that parliamentarians be able to pronounce on it, particularly in a minority government situation," the prime minister said, referring to the throne speech that will be presented when Parliament reconvenes. "We shouldn't be moving forward with an ambitious, bold vision to help Canadians and build a better future without ensuring that we have the support of Parliament."

The idea that MPs should be able to pass judgment on the government's agenda doesn't explain why all parliamentary business — including committee hearings into the WE affair — needed to be suspended for a month.

But Trudeau's acknowledgement that he'll need the support of at least one other party leads to another question: Is he interested in actually seeking out that support?

If the answer to that question is 'yes', circumstances may have created an opportunity for Trudeau's Liberals and Jagmeet Singh's New Democrats to find common cause.

The speculation around Parliament Hill lately has been all about the possibility of a federal election. Such speculation is both a reflex and a popular pastime whenever a minority government is in power.

A cease-fire on the centre-left?

But there's an obvious alternative to running another election campaign just a year after the last one: the Liberals could work with one or more of the other parties not only to pass the throne speech but also the policies and programs it promises.

The major federal parties don't have much of a recent history of working collaboratively. In fact, they have often seemed fundamentally incapable of cooperation — recall this summer's pitched fight over how the House of Commons should be conducting itself during a life-threatening public health crisis.

But the stakes of this moment — a senior Liberal recently described it as a "generational opportunity" to drive progress and change — might make the case for putting mutual contempt aside. At least for a while. And at least for a couple of parties.

The Liberals and Conservatives agree about little these days and probably see little to gain politically from cooperating with each other.  The Bloc Québécois already has indicated it will move a motion of non-confidence against the government this fall unless Trudeau resigns as prime minister (though it shouldn't be assumed that the Bloc won't drop that demand if it sees something it might gain by reversing course).

The Liberals and NDP: enemies with benefits

Barring a sudden change of heart by the Bloc, the Liberals seem to have one potential partner: the NDP. Together, the Liberals and New Democrats currently occupy 177 seats in the House, a comfortable majority with which to pass legislation.

The Liberals and NDP have some history in this respect. Not all of it is pleasant.

In 2005, Paul Martin's Liberal government needed support to pass its spring budget and found it in Jack Layton's NDP caucus. In return, the Liberals agreed to boost spending on affordable housing, education, training, the environment and foreign aid, while deferring a planned reduction in the corporate tax rate.

That spirit of mutual interest didn't last long. By the fall, the Martin government had signed the Kelowna Accord, which would have transferred $5.1 billion to Indigenous communities to address gaps in funding and welfare, and completed agreements with the provinces to provide $5 billion for child care and early learning. Stéphane Dion, the environment minister at the time, was pursuing regulations to reduce greenhouse gas emissions.

But the New Democrats joined the other parties in voting to defeat the Liberal government in late November 2005. The Conservatives formed government after the subsequent election and much of what the Liberals were pursuing was washed away.

Liberals took NDP for granted: Topp

The Liberal Party had been in power for a dozen years by then, so it's hard to take seriously any claims that they were hard done by when they were defeated in 2005. Brian Topp, the NDP's campaign director in 2005, has argued that the Liberal government's goal was a cynical attempt to move left and steal his party's support. Topp has said the parties fell out over federal health regulations. The NDP also was under pressure to withhold its support from a Liberal Party that had been deeply tarnished by the sponsorship scandal.

But progressives might still wonder whether meaningful things could have been accomplished if the Liberals and NDP had found a way to work together for longer.

Topp has argued that Martin's Liberals ultimately took the NDP's support for granted. "Our support, like any other, had to be earned and negotiated — by talking to us, by listening to us and by finding some compromise with us that we could accept," Topp wrote in How We Almost Gave the Tories the Boot, his account of another ill-fated attempt at partnership between New Democrats and Liberals — the 2008 coalition.

New Democrats might have decided to go into an election regardless. But Topp's point about the need for dialogue might be important; the work done between Liberals and New Democrats during Pierre Trudeau's minority government from 1972 to 1974 underscores the importance of opening lines of communication.

Trudeau's Liberals likely would want to be seen resisting the NDP's most extravagant demands. Singh's New Democrats surely would want to remain unsatisfied with whatever the Liberals propose.

But supporters of both parties likely share common goals now, such as greater access to child care, improvements to long-term care, reforms to employment insurance and new efforts to build a low-carbon economy.

Both parties might tell themselves that they could end up in a better position to advance their own specific agendas after another election. But an election is always a gamble.

The lesson of 2005 is that parties that fail to seize opportunities to make significant changes can end up waiting a long time for second chances — and in the meantime, big things can remain undone.