Steele's work remains fiercely controversial, to some a "dodgy dossier" concocted by President Trump's enemies.
But on this vitally important point - Kalugin's status as a "spy under diplomatic cover" - people who saw the intelligence agree with the dossier, adding weight to Steele's other claims.
But then they knew him already.
I understand - from former officials - that from 2013-16, Steele gave the US government extensive information on Russia and Ukraine.
This was work done for private clients, but which Steele wanted the US authorities to see.
One former senior official who saw these reports told me: "It was found to be of value by the people whose job it was to look at Russia every day.
"They said things like, 'How can he get this so quickly? This fits exactly with what we have.' It was validated many times."
http://www.bbc.com/news/world-us-canada-39435786