Special prosecutor Robert Mueller's investigation has proved "pretty pathetic," failing to probe all aspects of supposed collusion with Russia during the 2016 election, writer Ed Klein said Monday.

In an interview on Newsmax TV's "The Howie Carr Show," Klein said if Mueller did what he was supposed to,"he would look at the Democrats and Hillary [Clinton]," including their funding of opposition research that led to a notorious dossier on then-candidate Donald Trump — and alleged links between a 2010 uranium deal with Russia and the Clinton Foundation.

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"The clear need [is] for somebody to take a look at the Clintons, not [President] Donald Trump," declared Klein, the author of "All Out War: The Plot To Destroy Trump."

He said Monday's indictment of former Trump campaign manager Paul Manafort "reminds me of what happened in the 1920s when the FBI went after Al Capone."

"They couldn't find anything and they got him on tax evasion," he said. "And it's the same thing with Manafort."

"It's pretty pathetic, because the Mueller special counsel group is up for refinancing by Congress and I think he puts this out in order to show them he was doing something," Klein added. "But he's certainly not doing what he was supposed to do, which is look into Russian collusion."

"It seems to me that it's pretty darn clear from this dossier story that the Democrats were closer to the Russians than any Republicans were during the campaign," Klein added.

"Certainly the Clinton campaign was, we know it now because they paid for that dossier which was based on Russian misinformation."