Two months later, however, the BBC put out a story echoing Mensch’s original report about the Foreign Intelligence Surveillance Act (Fisa) court warrant issued in October to allow the justice department to look into transfers and communications between the Russian banks and Trump associate – and that US intelligence agencies were investigating the link.

The Guardian separately confirmed the original request for a Fisa warrant, which had been turned down earlier in the summer, and former officials said they believed that the Mensch and BBC account of the Fisa warrants was correct.

https://www.theguardian.com/us-news/2017/feb/17/louise-mensch-trump-russia-ties-media-scoop

Why was the first FISA turned down, in the summer?