The president’s decision on Saturday to lend the power of his office to accusations against his predecessor of politically motivated wiretapping — without offering any proof — was remarkable, even for a leader who has repeatedly shown himself willing to make assertions that are false or based on dubious sources.
It would have been difficult for federal agents, working within the law, to obtain a wiretap order to target Mr. Trump’s phone conversations. It would have meant that the Justice Department had gathered sufficient evidence to convince a federal judge that there was probable cause to believe Mr. Trump had committed a serious crime or was an agent of a foreign power, depending on whether it was a criminal investigation or a foreign intelligence one.
Former officials pointed to longstanding laws and procedures intended to ensure that presidents cannot wiretap a rival for political purposes.
“A cardinal rule of the Obama administration was that no White House official ever interfered with any independent investigation led by the Department of Justice,” said Kevin Lewis, a spokesman for Mr. Obama. “As part of that practice, neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen.”
https://www.nytimes.com/2017/03/04/us/politics/trump-obama-tap-phones.html