It's hard to say exactly what "living memory" should mean, but let's call it WWII. The worst would then be FDR, followed by LBJ or Obama. All caused great harm.
Nixon is an interesting one. The major screw up was relations with China. Other than that, he wasn't bad.
Thanks for the reminder.
FISA warrants cover two hops. If person Y communicates with both X and Z, a FISA warrant on person X will allow spying on person Z. In this case person X is Carter Page, and person Z is Donald Trump. It is certain that a suitable person Y exists. Such a person would be anybody who communicated, no matter how briefly, with both Carter Page and Donald Trump. Numerous journalists would qualify as person Y.