WASHINGTON — Mark J. Penn was one of the primary architects of President Bill Clinton’s re-election campaign in 1996 and served as chief strategist for Hillary Clinton’s presidential campaign in 2008. Few people have done more to advance the Clinton cause in the last couple of decades.

Which makes it all the more striking that in his current campaign the longtime Democratic political consultant has essentially switched sides and accused associates of the Clintons of helping to orchestrate a politically driven, manufactured “deep state” investigation into President Trump that Mr. Penn says should be shut down.

In a series of recent newspaper columns and appearances on Fox News, Mr. Penn has endorsed Mr. Trump’s argument that the investigation by the special counsel, Robert S. Mueller III, was instigated by secret Democratic intriguing. The inquiry, Mr. Penn said, has resorted to “storm trooper tactics” and has become a “scorched-earth effort” to “bring down Donald Trump.”

“This process must now be stopped, preferably long before a vote in the Senate,” he wrote in a column in The Hill newspaper that was posted on Sunday evening and generated a lot of buzz in Washington. “Rather than a fair, limited and impartial investigation, the Mueller investigation became a partisan, open-ended inquisition that, by its precedent, is a threat to all those who ever want to participate in a national campaign or an administration again.”