President Trump's allegation that Trump Tower was wiretapped by the federal government during the 2016 election is possible, digital surveillance experts tell Politico, but his claim that former President Obama personally ordered the surveillance doesn't match legal realities. The president cannot simply ask for a wiretap warrant the way Trump's tweets suggest; that is the role of law enforcement agents by way of a judge's order.
Still, there are other ways Trump Tower conversations could have been monitored by the feds:
First, they may have come upon Trump Tower phone calls if a targeted foreign agent was on the other end of the line — this method comes from the Foreign Intelligence Surveillance Court. Or Trump Tower digital chatter might show up while digging through the vast quantities of data hoovered up via more sweeping foreign surveillance programs.
Second, the FBI could have also asked for a so-called "pen register" or "tap and trace device," which only record the parties involved in a phone call. These requests have a lower bar for approval. [Politico]
All told, said Cindy Cohn of the Electronic Frontier Foundation, a digital privacy advocacy group, it is "very likely that the people in the Obama administration had access to the communication of senior Trump officials in the run-up to the election, because they have very, very broad authority." That would be the case regardless of the sort of political interference Trump suspects.
Notably, the Obama team's statement in response to Trump says "neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen," a denial that does not preclude the sort of access Politico describes.