At the G20 conference in Turkey, reports suggest that Prime Minister Justin Trudeau spoke eloquently and strongly at a closed-door meeting about the need to defeat the Islamic State of Iraq & the Levant (ISIS). The prime minister, it's said, pledged that Canada would play a part in that effort. Hopefully, the reports are true. ISIS is a threat to all civilized people and has explicitly threatened to attack Canada and its allies. We should play a part in the international campaign to contain and defeat this menace. But for Trudeau and the Liberals, tough talk must be met with action — and the action should come soon. France has already stepped up its assault on ISIS — apparently with the co-operation of the United States. François Hollande, the French president, has said that his country is at war with ISIS, and there remains the possibility that France will invoke Article V of the North Atlantic Treaty, of which we are signatories. If so, the Trudeau government could find itself obligated by treaty to acknowledge that it is at war with ISIS. As columnist Michael Den Tandt noted in these pages yesterday, Trudeau may not have ever imagined himself as a wartime prime minister. But he doesn't get to choose. Our ally has been attacked, viciously, in its own capital. If France chooses to go to war over this, even against an unconventional enemy such as ISIS, there is a legal and moral case to be made that Canada must go too. Indeed, Canada is arguably already at war with ISIS. There has been no official declaration, of course. But six Canadian CF-18 jets have been striking ISIS targets in Iraq since last year, and Syria more recently. A small contingent of Canadian special forces soldiers have been working with Iraqi forces and Kurdish militias to whip those local units into a coherent and effective anti-ISIS force (the rout of ISIS at the strategically important Iraqi city of Sinjar, which was retaken by Kurdish forces in recent days, gives hope that these efforts are paying off). There is an uncomfortable fact hanging over the head of Trudeau, however. Even while our allies are ramping up attacks against ISIS, he has pledged to bring our jets home from the fighting. He says Canada will do more to assist in training local ground forces, and that's all to the good, but that still means that Canada, at best, will end up doing roughly the same. Doing more on the ground while we do less in the air is effectively a cancel-out. By all means, relocate some (properly selected and vetted) refugees to Canada and do more to help train local forces on the ground. But why recall jets that are already there? Trudeau said on Monday that most Canadians voted to end the combat mission. Enough Canadians voted for Trudeau to give him a majority government — that much is certainly true. But polls have suggested strong support for our air campaign against ISIS. And that was before the atrocity in Paris. Circumstances, in other words, have changed, at least in terms of our allies' expectations, and there would be no shame in Trudeau deciding his position should change, too. The problem here, of course, is that Trudeau has never articulated a position, per se. He was admittedly clear that he'd bring the jets home. But neither he nor a member of his government has ever articulated why, having already committed its CF-18s to battle, Canada should bring them home. The closest he came was musing about Western military interventions in the Middle East posing risks of blowback, and saying that his predecessor, Stephen Harper, had never made the case for sending the jets in the first place. To the first point — it's certainly true that every intervention carries risks of unintended consequences, though that applies as much to a ground training mission, especially an expanded one, as an air campaign. Trudeau's concerns about blowback are incompatible with his assurances that Canada will continue to play a part, on the ground, to defeat ISIS. To the second point, even if Harper had failed to articulate a rationale for the combat mission (he didn't, but even if), the jets are there. They are hitting targets. They are aiding our allies. Bringing our fighters home is as much a choice as sending them in the first place, and the Liberals, either while campaigning or now in government, have yet to offer a definitive explanation as to why Canada should not be bombing ISIS. "Because Stephen Harper did it" isn't a good enough reason. The issue may not have gotten much attention during our recently concluded election campaign, but you can rest assured that our allies are watching closely. Pulling the CF-18s out now would send a terrible message to them about Canada's real willingness to stand by our friends in times of need. Our contribution is not huge. But it is real, and now is no time to do less. Canada is a rich and generous country. Our armed forces, though too small, are very capable. In the aftermath of Paris and ISIS threats of more attacks to come, absent a clear reason why they must return home, our planes should stay in the fight.