Sen. John McCain today called a Newsweek article alleging tensions with Mitt Romney's presidential campaign "liberal left-wing trash."

In the exclusive article, Newsweek Washington bureau chief and media critic Howard Kurtz reports that McCain has failed in his efforts to counsel Romney and is frustrated with his behind-the-scenes role on the campaign (Kurtz calls him a "caged lion").

"Four years after his own presidential bid, McCain’s luster as a Republican Party spokesman appears to have dimmed: a number of proposed campaign trips on Romney’s behalf have quietly evaporated, and there has been no offer of a speaking slot at the GOP convention," Kurtz writes. “'He’s chomping at the bit to do something,' a McCain aide confides."