MONTREAL—Prime Minister Justin Trudeau has not had that many good days over the past few months.

It speaks to the difficult year he has been having on the domestic front but also to the energy expended on the Canada/U.S. file by his government that Trudeau owes the best two of those days — over as many weeks — to moves by the Trump administration.

The lifting of punitive American tariffs on steel and aluminum provided the prime minister with a timely peg to bring the conversation back to bread-and-butter issues.

U.S. Vice-President Mike Pence’s visit this week allowed Trudeau to showcase the rainbow coalition he successfully held together in response to the U.S. demand that NAFTA be renegotiated.

And if Canadian voters needed a reminder of how difficult it is to keep track of the current U.S. administration, the immediate aftermath of that visit also provided it.

Pence’s whistle-stop in the federal capital was purportedly designed to oil the machinery for the swift ratification of USMCA — the trade deal that is meant to replace NAFTA.

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But no sooner had the vice-president boarded his plane to Washington than the White House was throwing a wrench in the operation.

Trump’s threat to impose tariffs on all Mexican imports into the U.S. is the latest move in his campaign to stem the flow of illegal immigrants making their way across the southern border. On that basis it is a bilateral issue between the U.S. and Mexico.

But it nevertheless increases the odds that roadblocks in Mexico City and on Capitol Hill will stand in the way of the ratification of the trade deal — and potentially even lead to its demise.

At this juncture, the fate of the accord is out of the hands of the Canadian government. Trudeau did not even get a heads-up from Pence about Trump’s imminent tariff threat on Thursday.

The whole episode has again highlighted the fact that no prime minister in recent history has had to deal with an American administration as unpredictable… and as inconsistent.

One of Trudeau’s most notable feats in these circumstances has been to avoid having the divisions that continue to plague Trump’s trade course in the U.S. be matched by similar divisions in Canada.

His handling of the NAFTA issue has earned him kudos from constituencies on the left and the right.

And yet if there is one file the Liberal party had no reason to be prepared to tackle when it first came to power in 2015, it was Canada/U.S. relations in general and the renegotiation of the country’s continental trade arrangements.

There certainly was no impetus on this side of the border to reopen NAFTA. No one at the bureaucratic or political level had really given the issue a lot of thought.

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Looking at the Oct. 21 election and based on the experience of Trudeau’s predecessors, the Canada/U.S. file could be a gift that keeps on giving for the Liberals.

Stephen Harper’s 2011 majority was, in no small part, built on his government’s management of the 2008 global financial crisis.

Jean Chrétien almost lost the 1995 Quebec referendum but was rewarded in subsequent elections for having changed the terms of engagement of the unity issue with the Clarity Act.

The negotiation that led to the 1988 free-trade agreement gave a sense of purpose to Brian Mulroney’s Tory government at a time when it was floundering under the weight of ministerial scandals.

As counterintuitive as it may seem, Canada’s governing parties — at least in the recent past — have often been more adept at dealing with the major challenges that have unexpectedly been thrown their way than at implementing some of their own signature campaign promises.

Here are two possible reasons for that.

Absent a line in the sand that they have drawn during their time on the opposition benches, governing parties are freer not only to think outside the box but to reach into the tool kits of their rivals.

Brian Mulroney’s Free Trade Agreement initiative was built on the findings of the MacDonald commission — a Liberal initiative.

Chrétien’s Clarity Act was inspired by the contention held by the Reform party that the federal government should set rules to govern a secession bid.

Deficit-spending as practised by the Harper Conservatives between 2008 and 2011 did not come to them naturally. Nor did auto bailouts. But there was plenty of opposition support for both.

And it is easier for a government backed by a professional civil service and with the capacity to tap — beyond partisan lines — into civil society for expertise to conceive complex policies than for a party to do so in opposition.

With a federal campaign just around the corner, this is a good time to remember that when it comes to crafting the signature promises that make up an election platform, branding and partisan calculations as often as not trump both reality and public policy imperatives.

Chantal Hébert is a columnist based in Ottawa covering politics. Follow her on Twitter: @ChantalHbert

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