So, would a second-order link be the launching pad for a legal surveillance of a US citizen? If Joe in NYC called Pavel, a Chechen activist who the NSACIAFBIOD

So, would a second-order link be the launching pad for a legal surveillance of a US citizen? If Joe in NYC called Pavel, a Chechen activist who the NSACIAFBIODNI is monitoring, is that sufficient basis for obtaining a warrant for monitoring all of Joe's communications? This is the sort of information we need.