On Saturday morning, as reporters scrambled to find sources for President Trump's allegation that his predecessor had wiretapped Trump Tower during the presidential campaign, it seemed all roads were leading to Mark Levin of Cheltenham.

"It began," the New York Times reported Sunday, "as a conspiratorial rant on conservative talk radio." Levin, a Philadelphia-born, Elkins Park-raised radio host with an enormous following, had spent much of his Thursday show alleging that the Obama administration had surveilled Trump and his associates during the campaign.

The far-right website Breitbart News -- where Trump adviser Stephen Bannon previously served as editor-in-chief -- picked up the story a day later. That story reportedly circulated around the White House, and on Saturday Trump started tweeting.

Since the president's explosive tweets, and the media frenzy that followed, Levin has contended that his assertions were based on reporting by the mainstream media -- and that he just connected the dots. (An Obama spokesman denied the allegations, and fact-checkers have reported that the evidence cited by Breitbart and others in the conservative sphere is sketchy at best.)

Levin is not a household name outside of conservative circles. "The most powerful conservative you've never heard of," the Daily Beast called him in a 2013 profile. But millions of people listen to his show each night.

He has said his conservatism dates to his upbringing in the Philadelphia region. In a 2007 interview with the Inquirer, he said a favorite pastime, as a teenager, was to visit Independence Hall and "imagine the founding fathers designing a nation."

Levin graduated from Temple University's Ambler campus at 19 and stayed at Temple for a law degree. He served for a time on the Cheltenham school board while in law school, he told the Daily Beast, and formed a tax-reform group called the Committee to Limit Taxation. He was the youngest member the school board has ever had, said Tom Ellis, the solicitor for Cheltenham Township's Republican organization.

"He created a lot of uproar, arguing for cutting taxes," Ellis said of Levin's time on the board. "He's a real conservative."

Though Levin, 59, is several years older than Ellis, they were both in the B'nai B'rith Jewish service organization as youths, Ellis said, and once, Levin took him to see Ronald Reagan speak. Levin would later join the Reagan administration, and became a familiar voice on talk radio in the waning Clinton years.

"He's always been an extremely conservative person," Ellis said. "It did surprise me" that he had moved into a radio career. "I was listening one day and they said, 'Mark Levin,' and I thought, is that my Mark Levin?"

Among the major themes of his show: that America is headed down a dark path and that liberals are trying to expand the federal government at liberty's expense. He's decried political correctness and accused politicians of downplaying the threat of terrorism. Last January, after a Philadelphia police officer was shot by a man who told police he pledged allegiance to the Islamic State, Levin spent a segment of his show criticizing Mayor Kenney's response to the shooting. Kenney had said the attack had "nothing to do with being a Muslim."

"A liberal, kook, pathetic, moronic, propagandist demagogue of a mayor," Levin called Kenney. He said he had uncles who had served in the Philadelphia Police Department, and he played "God Bless America" on the air in honor of them and other officers.