The carbon tax survived Saskatchewan. That was the easy part.

The Trudeau government's federal carbon-pricing backstop has survived to fight another day. And there are many, many more days left in this battle.

"The Greenhouse Gas Pollution Pricing Act is not unconstitutional either in whole or in part," a majority of justices on the Saskatchewan Court of Appeal ruled Friday, responding to a hostile reference from the government of Premier Scott Moe.

Three of the five justices took a look at Saskatchewan's arguments and found them wanting.

"Today's decision is a win for Canadians and for future generations," said Environment Minister Catherine McKenna.

It's a win for both Prime Minister Justin Trudeau and McKenna, as welland itbooststhe chances that one or both of them will still be in office come November.

There was alwaysmuch more to the Liberals' climate plan than the federal carbon price, of course, and a loss in Saskatchewan would not necessarily havescuttled anything. The Trudeau government surelywould have appealed to the Supreme Court in theevent of a defeat.

The planstill stands

But a negative ruling in Saskatchewan would have cast doubt on the viability of both the price and the plan. And much of the Liberals' argument on climate policy currently rests on the fact that they have aplan and Andrew Scheer's Conservatives do not.

That might change when the Conservatives do release a plan, something that's expected to happen sometime this spring. But even after the Conservatives explain themselves,the Liberals are likely to argue that their plan goes further toward meeting Canada's international emissions commitment for 2030. Theruling out of Saskatchewan doesn't make it any harder to sustain that argument.

It also doesn't make it any harder to be Justin Trudeau right now. The PM's re-election year got off to a poor start. It wouldn't have gotten any better for him if his government had been forced to explain why a judicial defeat was not a fatal setback. Trudeau needed a win and, in Saskatchewan's defeat, he found one.

This isn't the end, of course far from it. Premier Moe quickly signalled his government's intention to appeal the ruling to the Supreme Court. And the Ontario Court of Appeal just finished hearing arguments in Premier Doug Ford's challenge of the federal carbon price. Still to come is a challenge fromBrian Pallister's government in Manitoba;Jason Kenney's new government in Alberta is likely to file a challenge of its own.

And there's still that federal election, of course. "Ultimately, the fate of the Trudeau carbon tax will be decided in the federal election this fall," Moe said on Friday.

The high political cost of doing something

In that election, Trudeau will have to contend not only with the opposition of the federal Conservativesbut also with the stickers that Ford's government is trying to affix to every gas pump in Ontario under penalty of fines.Premier Ford's people already have begun running radio ads against the Liberal carbon tax.

The history of climate policy in Canada is largely a story of federal governments musing aloud about the possibility ofdoing something, and then not doing it. Perhaps now we're seeing why.

The Trudeau government's plan for a federal carbon-pricing backstop made a good deal of sense in 2016 and 2017. British Columbia had adopted a carbon tax in 2008 and Quebec moved forward on cap-and-trade in 2012. The Ontario government announced its intention to pursue cap-and-trade in April 2015.

By the time the Trudeau Liberals came to office in November 2015, the new premier of Alberta, Rachel Notley, was ready to move forward with her own carbon tax. The four most-populous provinces had carbon-pricing policies and it made sense to build a national plan around those initiatives.

For a while, Saskatchewan was the only real voice of dissent. And if not for serious questions about Patrick Brown's personal conduct, Trudeau's plan for a national price on carbon might still seem relatively secure.

But then Brown had to resign and was replaced by Ford. And then a Liberal government in New Brunswick was defeated. And then Brian Pallister, who was once willing to put a price on carbon, got cold feet. And then Jason Kenney replaced Notley in Alberta. And now the federal backstop is likely to apply in five provinces, while just four provinces have carbon pricing plans of their own (Prince Edward Island has opted for a combination of federal and provincial policy).

Still, Moe's right to say that much rests on the federal election. A victory for Trudeau in October obviously would lend further political legitimacy to his approach. Several more years in office also would give Trudeauthe time and space to respond to any negative court rulings.

When Trudeauoriginally pitched his approach to climate policy in February 2015, he compared it to the introduction of medicare the result of a combination of federal leadership and provincial implementation.

Four years later, the better comparison might be to President Barack Obama'sefforts to expand public health care in the United States an arduous process, an imperfect result, the consumption of significant political capital, the vociferous opposition of political rivals and numerous legal challenges.

In Obama's case, he at least ended up with a major achievement:the most significant expansion of American health care in generations. Nine years after the Affordable Care Act was signed into law, Obamacare is still being attacked but it's also still working. His Republican successor has proved unable to completely repeal it, his Democratic successors are eager to build on it.

Trudeau might end up with something similar. But the court of public opinion gets the final word on him this fall. And that process is not always so judicious.