Special counsel Robert Mueller's Russia investigation began as opposition research helped by the Clinton Foundation and needs to end, former Clinton confidant Mark Penn argued Monday.

Writing for The Hill, Penn blasted the investigation on the Trump campaign.

"They started by telling the story of Alexander Downer, an Australian diplomat, as having remembered a bar conversation with George Papadopoulos, a foreign policy adviser to the Trump campaign. But how did the FBI know they should talk to him?" Penn wrote.

"That's left out of their narrative. Downer's signature appears on a $25 million contribution to the Clinton Foundation. You don't need much imagination to figure that he was close with Clinton Foundation operatives who relayed information to the State Department, which then called the FBI to complete the loop. This wasn't intelligence. It was likely opposition research from the start."

Penn also alleged that high-ranking officials at the Department of Justice and the FBI conspired to let Hillary Clinton off the hook regarding her use of a private email system while she was secretary of state.

"At this point, there is little doubt that the highest echelons of the FBI and the Justice Department broke their own rules to end the Hillary Clinton 'matter,' but we can expect the inspector general to document what was done or, more pointedly, not done," Penn wrote.

Penn is the chairman of the Harris Poll and was an adviser to former President Bill Clinton. More recently, he worked on Hillary Clinton's senatorial campaigns in 2000 and 2006, along with her 2008 presidential campaign.

His opinion story in The Hill, however, indicates that his feelings toward the Clintons have soured.

Regarding the Mueller probe, Penn said the "the 'deep state' is in a deep state of desperation. ... they know a reckoning is coming."

At President Donald Trump's request, the DOJ's inspector general will now investigate the FBI and whether surveillance on the Trump campaign began for political reasons.

Penn argued that current and former officials in the intelligence community and at the DOJ are trying to salvage their reputations.

Investigators continue to "come up empty," he wrote, adding that Deputy Attorney General Rod Rosenstein and Mueller's conflicts should disqualify them from the probe.

A dossier on Trump written by British ex-spy Christopher Steele encouraged the investigators, Penn wrote.

"Egged on by Steele, they simply believed Trump and his team must be dirty. They just needed to dig deep enough," Penn wrote.

"The less the investigators found, the more determined and expansive they became. This president and his team are now on a better road to put appropriate limits on all this," Penn added, calling the probe a "partisan, open-ended inquisition."

Trump should testify and Attorney General Jeff Sessions should take action to "take back his Justice Department," Penn argued.

"Stopping Mueller isn't about one president or one party. It's about all presidents and all parties. It's about cleaning out and reforming the deep state so that our intelligence operations are never used against opposing campaigns without the firmest of evidence," Penn wrote.