It's hard to understand what congressional Democrats hope to achieve by summoning a reluctant Robert Mueller to appear before the House Judiciary and Intelligence committees on Wednesday.

The former special counsel's exhaustive 448-page report has been done for nearly four months. It's been public for three, with the country having plenty of time to absorb its comically anti-climactic conclusion that, although the 2016 Trump campaign did a lot of shady, underhanded things, none of them technically amounted to criminal conspiracy (collusion) with the Russian government, and that, although there was substantial evidence of obstruction of justice on the part of President Trump himself, none of it is actionable because sitting presidents can't be indicted. The whole absurd, convoluted result was perfectly summarized in Mueller's oracular pronouncement at his press conference on May 29: "If we had had confidence that the president clearly did not commit a crime, we would have said so."

Mueller spent two years and about $35 million on an exhaustive investigation that did not conclude that the president was not guilty of some form of criminality.

So here we are, waiting for Democrats to question Mueller on the subject, even though he has made it quite clear that he won't answer any questions beyond the bounds of what's in the report itself. What's likely to come from that? Legally speaking, the answer is almost certainly nothing. And politically speaking? Maybe even less.

Of course some Democrats may hope that Mueller will drop his evasiveness and actually accuse Trump of a crime. None other than former FBI Director James Comey appears to believe precisely this. In comments on MSNBC's Deadline: White House with Nicolle Wallace on Tuesday night, Comey gave voice to this expectation, asserting that "if this were a case about somebody other than the president they'd already have been indicted on at least several of these obstruction incidents, maybe all of them."

Ah, I see. So you mean any random person who wasn't the president of the United States but who was nonetheless under special counsel investigation for conspiring with a foreign power to throw a presidential election and who then fired the FBI director and threatened the special counsel's investigation would be indicted for obstruction of justice? Don't be ridiculous. Every alleged act of obstruction on the part of Trump follows from the fact that he's the president of the United States and head of the branch of government that was attempting to investigate him. It's impossible to imagine the series of actions and events recounted in the section of the Mueller Report devoted to obstruction of justice involving anyone in the world other than the president.

Despite what Comey (and possibly some House Democrats) piously wishes to believe, Mueller will not, if pressed in questioning, "reach a decision that there is sufficient basis to charge the president." If Mueller thought he could do that, he would have done so in the report.

So much for legalities. When it comes to politics, Democrats seem at first to be on firmer ground. Impeachment, not indictment, is the way for them to bring Trump down, and impeachment is fundamentally a political act, not a legal one. Moreover, Mueller has already implied that his report contains more than enough material to justify political action.

Yet nothing Mueller says on Capitol Hill is likely to build momentum toward that end. If the past two and a half years have taught us anything, it is that in a time of intense partisan polarization, political neutrality is the empty set. In order to maintain his aura of objectivity and impartiality, Mueller needs to say nothing that can be construed as an attack on the president. The moment he says something that appears to be partisan — with partisanship defined as anything that helps or hurts one party or the other, quite apart from its truth or falsity — he becomes another political player, another political operator out to advance his interests and agenda.

This helps to explain why the Mueller report is written the way it is, with such punctilious impartiality that it appears to arrive at no definitive conclusion on the very issues Mueller was tasked with investigating. If you take in the multitude of dots and put them all together, the report can look bad for Trump and the people around him — but it can also look like a great big nothing. The effort of judgment falls and depends on who the reader is. Is the reader a Democrat who's disliked Trump from the very start and tended to assume the very worst about him, his motives, and his actions? Or is the reader a Republican who's inclined to give the president the benefit of the doubt, not necessarily out of any affection for the man but simply as a means to maintain the party's hold on power?

On Wednesday, Democrats will do their best to pull Mueller over to their side, pushing him to declare that his findings confirm their suspicions about the president and justify their desire to see him removed from office. To which Mueller is likely to respond, by implication at least, that it isn't his place to render that judgment — that the judgment has to be made by those posing the question. He has provided them with the evidence. The rest is not his business.

At a less polarized time, Mueller might not have felt so constrained. His effort at objectivity wouldn't have required that he transform himself into a nullity who speaks in riddles and deploys double negatives. He'd be able to assume that public-spirited individuals from both parties would want to discover the truth and render judgment, regardless of which party gained and lost from the outcome. But that isn't the time in which we live.

In our time, Mueller's congressional testimony will add nothing to his report, and Democrats will find themselves at the end of the day exactly where they were at the beginning — longing to impeach the president but lacking public support sufficient to make it politically wise to do so.