Martin Luther King, targeted for surveillance by the then head of the FBI Edgar Hoover. Photograph: Michael Ochs Archives
Among those was Martin Luther King, who the head of the FBI, Edgar Hoover, suspected of being influenced by communists. Hoover asked the then attorney-general Robert Kennedy in 1963 to authorise surveillance requests to install bugs in his home, office and hotels where he stayed on trips. No evidence ever emerged linking King to communism, but they did record at least one sexual encounter.
Throughout the 20th century there were intermittent challenges in Congress and the courts attempting to redress the balance between intrusive surveillance and the right to privacy. Amid the panic in the Bush administration in the aftermath of the 9/11 attacks, the president secretly sanctioned warrantless wiretapping surveillance of phones, the internet and any other electronic communications without the need for a warrant. When this was revealed in the New York Times in 2005, the Bush administration reversed the order and there was a return to warrants.
This row was dwarfed in 2013 when the National Security Agency whistleblower Edward Snowden revealed the scale of mass surveillance the agencies prefer bulk data collection not only of foreigners but of US citizens, which the intelligence agencies had publicly denied up until that point.
Among the many intercept programmes revealed by Snowden was Tempora, run by the NSAs UK counterpart GCHQ, and shared with the Americans. This was a kind of wiretap on a scale that would have been beyond the imagination of the American civil war soldiers who climbed telegraph poles, or the FBI agents breaking into Kings hotel room to plant a bug.
GCHQ placed intercepts on the network of fibre-optic cables that carry much of the worlds internet traffic, offering a window into the world of an estimated two billion users of the worldwide web.
The US intelligence agencies have so far made a distinction when denying surveillance of Trump. There have been no denials about surveillance of those associates who might have been in contact with Russians. Those kind of contacts would be relatively easy to establish, not through break-ins or even physical surveillance which has not been made redundant by the digital age, with agencies running teams trained in following targets without, hopefully, being seen. With so much information hoovered up and available to the agencies, all they have to do is sift through those communications to establish the extent if any of links between Russia and Trumps team.