Which is the greatest 'witch hunt' in US political history?

Related Link How Mueller’s First Year Compares To Watergate, Iran-Contra And Whitewater (FiveThirtyEight)

Applying Trump's term to all special investigations curated by the National Archives and measuring them by time alone, Trump's would not yet be the greatest witch hunt in American history.

Turns out that witch hunts drag on for years and years. And years. 

One complaint about the Mueller investigation is that it appears to have followed lines away from its original mandate on collusion.

That's also a trait shared by those other two most notable special investigations, which after years of work led to Nixon's resignation and President Bill Clinton's impeachment. There are differences, obviously, in terms of alleged wrongdoing, the laws -- now lapsed -- under which special prosecutors were appointed and other things. 

But objectively speaking, five of the last nine presidents -- including Trump -- have been ensnared somehow in drawn-out independent investigations, assuming that the Iran-Contra affair also touched George H.W. Bush. There was a boom of smaller independent investigations into a number of Reagan administration officials. But each of the big investigations that bear some resemblance to Mueller's lasted years from start to finish.

Kenneth Starr, the nemesis of Clinton leading up to his impeachment, was one of three people to fill the role of independent counsel investigating him. The Whitewater probe largely wrapped with the publication of the Starr report and his recommendation that Clinton be impeached, but the office carried on for years, issuing reports years after Clinton left office in 2001.

The National Archives has documents from that investigation that span a decade and represent 3,149 cubic feet. Yes, apparently they measure these things in cubic feet, as in a foot-tall box of foot-long file folders. The Whitewater investigation was first empaneled in 1994, the second year of Clinton's presidency, and extended for years past his impeachment and subsequent acquittal in the Senate in 1999.