* 'Remember the Maine' instigated the Spanish-American War, but much evidence says the Maine was destroyed by accident. William Randolph Hearst, a leading publisher of yellow journalism, famously promised a compatriot: "You furnish the pictures and I'll furnish the war".
* The Gulf of Tonkin incident instigated American involvment in the Vietnam War.
* Iraq's weapons of mass destruction program, which didn't exist, instigated the Iraq War.
In today's case, I trust the source much less than many of those who have made prior errors. I also note that it was a the head of Homeland Security, a political appointee, who made the accusation. It was not the head of the FBI or an intelligence agency; it is not represented, at least in the reporting I've seen, as a consensus of the US intelligence community; I also note that the White House has left some distance between itself and the accusation - it's not made by the President or his National Security Advisor, for example.
Also, the very serious accusation rings of hype. North Korea has acted especially badly, largely unchecked, for more than a decade, which is false and a political swipe at the prior President. If that part of the accusation is exaggerated and political, I wonder about the other parts, and I wonder about the accusers ability or willingness to separate politics from very serious policy.