PALM BEACH, Florida: President Donald Trump has accused former President Barack Obama of ordering Trump’s telephones tapped during last year’s election, but Trump is not offering any evidence even as he makes politically charged references to Watergate, Nixon and McCarthyism.

An Obama spokesman said the assertion being made against the former president was “simply false.” Lawmakers from both parties called on Trump to offer proof and to say publicly what he knows.

In a series of morning tweets Saturday, Trump suggested Obama was behind a politically motivated plot to upend his campaign. He compared the alleged events to “Nixon/Watergate” and “McCarthyism!” And he called Obama a “Bad (or sick) guy.”

The Watergate break-in during the Nixon administration led to President Richard Nixon’s resignation and the conviction of several aides. Republican Sen. Joe McCarthy’s reckless and unsupported charges of communist infiltration in federal government during the 1950s gave rise to the term “McCarthyism.”

After Trump’s well-received speech to Congress on Tuesday, the tweets reflected the president’s growing frustration with the swirling allegations about his advisers’ ties to Russia, which are under FBI investigation, and his team’s inability to overcome them,

Obama spokesman Kevin Lewis said a “cardinal rule” of the Obama administration was that no White House official ever interfered in Justice Department investigations, which are supposed to be conducted free of political influence.

“As part of that practice, neither President Obama nor any White House official ever ordered surveillance on any U.S. citizen,” Lewis said, adding that “any suggestion otherwise is simply false.”