What crimes could have been committed? Ironically, for Democrats falsely accusing Attorney General Sessions, perjury and conspiracy to commit perjury, as well as intentional violations of FISA. Rather shockingly, no law currently forbids misusing the power of the presidency to spy on one’s adversaries. What the law does forbid is lying to any judicial officer to obtain any means of surveillance. What the law does forbid, under criminal penalty, is the misuse of FISA. Both derive from the protections of the Fourth Amendment itself. Under section 1809, FISA makes it a crime for anyone to either “engage in” electronic surveillance under “color of law” under FISA without following the law’s restrictions, or “disclose” or “use” information gathered from it in contravention of the statute’s sharp constrictions.
FISA, 50 USC 1801, et seq., is a very limited method of obtaining surveillance authority. The reason for its strict limits is that FISA evades the regular federal court process, by not allowing regularly, Constitutionally appointed federal judges and their magistrates to authorize surveillance the Fourth Amendment would otherwise forbid. Instead, the Chief Justice handpicks the FISA court members, who have shown an exceptional deference to the executive branch. This is because FISA court members trust the government is only bringing them surveillance about pending terror attacks or “grave hostile” war-like attacks, as the FISA statute limits itself to. Thus, a FISA application can only be used in very limited circumstances.

http://www.usasupreme.com/fbi-twice-refused-wiretap-trump-obama-went-around/