One of the most energetic and successful rightwing talk radio hosts has been on the attack despite the slim basis for his claims – and Donald Trump is listening

The ultimate source of Donald Trump’s wiretapping allegations – which he has presented without evidence – is one of the most prominent conservative broadcasters in the country. Yet compared with such colleagues as Rush Limbaugh or Glenn Beck, few liberals have heard of him.

On Friday, Breitbart News reprinted and amplified allegations of an attempted “silent coup” by the Obama administration, which were reportedly the basis of Trump’s tweets about wiretapping on Saturday. But Breitbart acknowledged in its reporting that the case was first made on Mark Levin’s radio show on Thursday night.

Levin stitched together material – including from the New York Times, the Washington Post, and the Guardian – on Foreign Intelligence Surveillance Act (Fisa) court warrants sought during the election. In some cases, the reports he cited were simply mentioning unconfirmed information from sources such as the rightwing tabloid site Heat Street. But Levin went on to claim that the Obama administration had used “police state” surveillance tactics against the Trump team.

Despite the slim basis for his claims, Levin has been on the attack in the first part of this week, writing open letters to reporters who have questioned his stories, and lambasting others on air.