Now Ottawa. As gunfire echoed at the National War Memorial and inside Parliament's halls, the capital of Canada joined a growing league of cities that has felt the brunt of a nihilistic violence metastasizing across the globe.
As details unfolded, we learned that Cpl. Nathan Cirillo, 24, an Army reservist, was killed on guard duty at a monument honoring Canada's war dead. We were told the shooter, who was also killed, was Michael Zehaf-Bibeau, 32, a Canadian who converted to Islam.
What's not fully clear for now is how many people were involved in the attack and what motivated them.
But we strongly fear this was an act of terrorism.
The last few decades have seen a long series of heinous ideological attacks on civilized societies -- whether in Manhattan's financial canyons; or against the Pentagon, just a stone's throw across the Potomac from Washington; or deep within the London tubes; or inside a luxury hotel in Mumbai. We don't expect the carnage to end soon.
So unfortunately, police must constantly search for new ways to keep our guard up -- in Ottawa, 75 miles from the New York State border, and here in New York City.
As Wednesday dawned, Canada's Parliament was on just a "medium" security alert, because Canadians worried about an overzealous response to threats, an official said.
That's a noble concern. But here's a cautionary tale: As New York's mayoral race raged through the summer of 2001, at least one candidate promised that, if elected, he would tear down -- "with a front-end loader" -- the wrought-iron security fence around City Hall. A few days later came 9/11. Security is tighter than ever now.
The United States and Canada have work to do. We must keep our eyes on "jihad tourists" -- our own citizens who visit global trouble spots and come back radicalized against us. But we also have to do it legally. And as we struggle to keep public buildings open, consistent with our splendid democratic traditions, we must also make sure we keep terrorists out of the hallways and our people safe.
Both nations must protect their citizens in a world gone mad -- without going mad themselves. It's not so easy.