Ottawa and Queen’s Park aren’t always going to get along this well. Both governments have a responsibility to defend their respective interests, which often are not directly aligned. All governments must be prepared to defend the interests of all of their citizens, and the interests of a province — even the country’s biggest one — do not always fit with the priorities of the entire country. And both governments must be prepared to walk away from collaboration if it’s not fully in the best interests of their respective constituencies.

It is this need for boundaries that made Prime Minister Justin Trudeau’s decision to actively campaign for the Ontario Liberal Party last week more damaging than simply creating a perception of undue partisanship. Trudeau spent his Tuesday evening in a Whitby sports bar alongside Ontario Premier Kathleen Wynne and Liberal candidate Elizabeth Roy ahead of last week’s by-election in the provincial riding of Whitby-Oshawa.

Trudeau’s barnburner speech, which failed to lift Roy to a win in the long-time Progressive Conservative riding, turned out to have nothing to do with what he’s been up to in his first 100 days in office. Instead, Trudeau just recycled the vague slogans he used last fall.

“In the last election, hope trumped fear … Ya think that people would have learned from that,” he said, according to The Globe and Mail. “We’ve seen some folks out there who still need to learn. So let’s teach them a lesson!”

But the federal election ended almost four months ago, while the last provincial election campaign was a year and a half ago. Both leaders now run majority governments. Both have a long list of unmet promises.

Trudeau and Wynne aren’t a political tag-team. While the cooperative spirit might serve short-term goals for each, it can run contrary to the need to keep their respective offices and responsibilities separate from each other. Their interests really are vastly different, and they require debate and a necessary degree of combativeness. And if the public is to be allowed to make informed judgements, it’s better that the debate takes place openly instead of being covered up to maintain partisan amity.

Take a brief look at the files Trudeau and Wynne want to tackle while they’re in power — and consider the likelihood that the Ottawa-Queen’s Park relationship will continue on a friendly path.

Climate change has wound up national anxiety over western alienation just as the oil sector is going through the wringer. Trudeau faces a tough job in wrangling provinces which all want to decrease emissions at different rates. At the end of the day, he has to frame this patchwork as something that works in the national interest, as his natural resources minister is fond of saying. If his solution looks like the option favoured by Ontario over other regions, Trudeau will be accused of playing favourites.

Planned infrastructure spending is going to hit the federal budget under conditions that will be much more dire than they were when it was promised. On Thursday, Trudeau told La Presse that the federal Liberals will accrue more than the $10 billion in deficit planned for 2016-17. This comes on the heels of the drop in oil prices and the Liberals having to revise the budget for the current year. Ottawa has to shave its campaign promises one way or the other, or risk breaking the bigger promise of a balanced budget ahead of the next election.

The axe could fall on social benefits, such as Wynne’s long-sought expansion of the Canada Pension Plan. She has spent the greater part of her time in office fostering a consensus around her vision of a larger role in the pension business for government — not to mention a reinvestment in infrastructure. Trudeau has to balance these election promises against his dwindling pocketbook, a problem that has national implications.

Working with like-minded leaders can be a useful shortcut in politics; (Who can forget former prime minister Stephen Harper calling a potential win by former Ontario Progressive Conservative leader Tim Hudak a “hat trick” while Rob Ford was still mayor of Toronto?)

But campaigning together for a cause that doesn’t deliver substantive change for voters makes it easy to think the bonhomie is more about building a stronger Liberal brand than a stronger country and province. To get things done in politics, sometimes even friends have to be able to disagree in public.