What's Crossfire Hurricane?

The FBI opened a foreign agents registration act investigation on July 31st, 2016. The point of that investigation was to determine whether individuals associated with the Donald J. Trump for president campaign were coordinating activities with the Russian government without having registered as agents of a foreign power. Outgoing Republican Senate Judiciary Committee Chairman Lindsey Graham said about crossfire hurricane: "I consider the crossfire hurricane investigation a massive system failure by senior leadership"