Any ‘bugs’ could be very low tech devices, simple audio recorders rather than transmitters, placed and retrieved by hand on a regular basis.
Then again, there could be a team of “remote viewers” paid to do nothing but spy on Trump and his administration.
In the digital age no one needs to "plant" a device. Digital phones and other smart devices can be hacked to come on without a call or piggybacked to provide a monitor post. In the 1980,s we could bridge a maintenance station on a Northern Telecom or DSC (Alcatel - Nokia) Long Distance switch to monitor individual phone calls. Yes, maintenance technicians listen to phone calls. A technician on the graveyard shift has been known to monitor the Trunk lines between New York and Miami and put the calls on the building intercom just to stay awake. Anyone can be spied on.
It is a simple thing for an expert to use the digital world as a vast spy network.