According to the letter of the law, the federal government has the power to push through projects like the Trans Mountain pipeline expansion, allowing the movement of Alberta oil through British Columbia to the Pacific.
Ottawa has the power – and abundant reason for caution.
On the one hand, Prime Minister Justin Trudeau can't just abandon Alberta oil, and the Canadian economy can't endure that oil being frozen in, to be replaced by supply from other countries.
On the other hand: politics. Politicians tend to be reluctant about putting themselves offside voters. The federal Liberals hold nearly half the seats in B.C., with most in and around Vancouver, where pipeline opposition is strong.
But if the Trans Mountain expansion can't be built, can any pipeline? That's not a rhetorical question. There's already an existing pipe on the route, and has been for decades. At its terminus, there are already tankers carrying oil from Burnaby to the sea. This is the least intrusive pipeline proposal out there.
Well before the recent provincial election, the Liberal government of B.C. had given its consent to the Trans Mountain expansion. But a minority government, the election's likely outcome, has reopened the issue.
Constitutionally speaking, the federal government has the power to green-light a pipeline. If it wants to force a project through, Ottawa can even turn to Section 92.10 of the Constitution, which gives the federal government the power to ensure the construction of any works it declares to be "for the general advantage of Canada."
However, that clause hasn't been called on in decades. The conflict between Quebec and Ottawa made using it unwise, even in a province other than Quebec. It's still valid law, but invoking it now, after decades of dormancy, would be a shock to Canadian politics.
But leaving Alberta oil landlocked and stuck in that province, due to an inability to build the most safe and efficient means of oil transport, would be shock to the economy.
The Trudeau government would like to both move oil, and win applause from those who oppose moving oil. That's no longer possible. Ottawa needs to handle things with subtlety, delicacy and diplomacy – but it is going to have to choose.