“You are not alone,” Glenn Beck likes to say. For the disaffected and aggrieved Americans of the Obama era, he could not have picked a better rallying cry.

Mr. Beck, an early-evening host on the Fox News Channel, is suddenly one of the most powerful media voices for the nation’s conservative populist anger. Barely two months into his job at Fox, his program is a phenomenon: it typically draws about 2.3 million viewers, more than any other cable news host except Bill O’Reilly or Sean Hannity, despite being on at 5 p.m., a slow shift for cable news.

With a mix of moral lessons, outrage and an apocalyptic view of the future, Mr. Beck, a longtime radio host who jumped to Fox from CNN’s Headline News channel this year, is capturing the feelings of an alienated class of Americans.

In an interview, Mr. Beck, who recently rewatched the 1976 film “Network,” said he identified with the character of Howard Beale, the unhinged TV news anchorman who declares on the air that he is “mad as hell.”