The inside story of how the Liberals and NDP faced a crisis that shook their alliance — and why Justin Trudeau’s government survived it

OTTAWA—There were supposed to be no surprises.

It’s the bedrock of the Liberal-NDP deal — a simple notion that, despite the two parties’ competing political interests, neither would ever catch the other off guard.

But eight months into the governing agreement that could see the NDP prop up the minority Liberals until 2025, that principle was violated.

The Liberals had quietly introduced a series of amendments to their firearms bill. And the New Democrats were blindsided.