The United States Foreign Intelligence Surveillance Court (FISC, aka the FISA Court) oversees requests for surveillance warrants against foreign spies inside the United States.
As of 2013, the FISA court denied only 12 warrants since its inception. It has granted over 34K requests since its inception.
At the heart of the probes against President Donald Trump is the FISC approval of the surveillance of Donald Trump & his associates.
Based on the FVEY monitoring system run by Australia, Canada, New Zealand, USA & UK a suprious dossier was created & marketed by Sen John McCain. This dossier created by former MI6 operative, Christopher Steele, was the purported evidence for the justification of the Trump surveillance.