Democrats in Congress are eager to have Special Counsel Robert Mueller testify publicly. But Mueller is dragging his feet \u2014 and making a big mistake.New York Rep. Jerry Nadler, the Democratic chair of the House Judiciary Committee, gave his most extensive comments on the negotiations around Mueller's pending testimony thus far Thursday night on Rachel Maddow's show.He said the Mueller is reluctant to testify in public because he "doesn\u2019t want to participate in anything that he might regard as a political spectacle.\u201d Instead, Mueller would like to testify to the committee privately. "He envisions himself, correctly, as a man of great rectitude and apolitical," Nadler said.My first reaction to this was simple: Tough. When Mueller was running the investigation, it was up to him to decide how public he wanted to be. Now that it's over, if Democrats in Congress want to call him for a hearing that they use to further political talking points, that's their choice. Mueller doesn't get to be the ultimate arbiter of what is and isn't political. And he's not a flower that will wilt with too much exposure.But there's also a more reasoned, thoughtful argument that I think could persuade Mueller to testify publicly, even despite his hesitations. He had the discretion and wisdom to keep his head down and remain silent during the Russia investigation, a decision that gave him both a mystique and an above-it-all respectability while the president was attacking him that surely worked to his benefit. This was a smart, prudent move that served to preserve his credibility.That credibility, however, only matters if people have the chance to hear and believe what he has to say. Almost no one in the country who doesn't write about or do politics for a living is going to read a 400-page report. Few would read the transcript of a closed-door hearing.But if Mueller actually gets the chance to describe his work, defend it from combative Republicans, explicate its most important parts when pressed by Democrats, and explain exactly why he made the choices he did, people will listen.It will be a spectacle. But he will largely be in control, and he can stick to the facts he wants to stick to.Mueller likely just sees his role as that of a narrowly constrained prosecutor. His job was to find the facts and to bring the charges he thinks were worth bringing. Having done that, he thinks it would be inappropriate to promote his findings or be used as a political tool. In the report, he was clear that, with regard to his obstruction of justice investigation of President Donald Trump, his role was to find facts for Congress and potentially future prosecutors to consider. Now that the report is public and in the hands of Congress, he concludes, his job is done.But even as a narrow fact-finder and fact-sharer, his job is not done. It's true that it's Congress's role to impeach if necessary based on his findings, but Congress is constrained and guided by the public. For the Congress to do its job, both lawmakers and the public at large have to be educated about what the facts are. Burying the facts in a dense report leaves much of the education of the public undone. Mueller is uniquely situated to educate the public about the report by testifying publicly.And in fact, Mueller must correct the record. Trump and his supporters \u2014 including Attorney General Bill Barr \u2014 have lied and misled the public extensively about the report and the investigation. Trump has lied about and endlessly smeared Mueller himself. Mueller's job isn't done until he has helped debunk and challenge these lies.Obviously, this is not a role Mueller wants to play. It will, inevitably, turn him into something of a political figure. But even if he just sees himself as a prosecutor and fact-finder, challenging lies remains a central part of his duty. Defending his work is part of his duty. He will surely insist that it's not his call whether Trump deserves to be impeached \u2014 but he has an important role to play on behalf of those who make that decision.Somewhat ironically, Mueller could learn something from former FBI Director James Comey. Comey has been extensively criticized for his tendency to make public pronouncements about federal investigations \u2014 and I certainly agree that he made mistakes by going too far in this direction. But Comey understood and understands the power and the importance of speaking publicly \u2014 even engaging in a bit of spectacle \u2014 when needed. Mueller could learn something from that.