Robert Mueller's appearance in Congress this week will be a hinge moment — the question is which way it might swing the political trajectory in Washington.
The Democrats who have negotiated for months to get Mueller to appear, and wound up compelling him with a subpoena, want Americans to watch the former special counsel tell his story on Wednesday in TV-friendly soundbites that erode support for President Trump.
The Republicans who've excoriated Mueller, his investigation, the Justice Department and FBI for months will have their Public Enemy No. 1 captive before them in the witness chair. They want to tar and feather him before closing the books on what they've called the Russia "hoax."
As usual, reality likely will fall somewhere in between these extremes, but the precise importance of Mueller's hearing and what follows depends on the specifics of what takes place.
Here's what's at stake.
Election security legislation
National security officials warn that election interference like that waged against the U.S. by Russia in 2016 hasn't gone away and likely will return through the 2020 presidential election.
But even though intelligence and law enforcement agencies, elections supervisors and many voters are better prepared than they were, the legal and legislative environment in the U.S. is broadly unchanged.
Some members of Congress have offered proposals that range from more security funding to mandating paper ballot backups to requiring campaigns to report contacts with foreigners. So far no major bill has been passed.
One big question about Mueller's testimony is whether he will change the political state of play enough to clear the way for new legislation.
Senate Majority Leader Mitch McConnell, R-Ky., in particular, has been cool to any election legislation in the upper chamber.
And although the Democrats, who control the majority in the House, and a few key House Republicans have said they want some kind of election security bill, no consensus proposal has surfaced.
Even if one did, there would still be the task of reconciling it with McConnell's Republicans and getting Trump to sign it.
Will Mueller change enough minds on Capitol Hill? Or if Mueller Day results in the status quo, will that finally shut the door to any bill passing by Election Day?
What, exactly, did Mueller's office investigate?
For Democrats who have staked their political strategy on new investigations of their own into Trump, those details are critical.
Trump and his Republican supporters have said the results of Mueller's investigation are a political inoculation that resulted in a clean bill of health for the president. Trump, for example, has said that he assumes Mueller obtained his tax returns — which Trump has not released, unlike many of his predecessors — and investigators evidently didn't find anything amiss.
Is that so?
If Mueller establishes as much, that would take the wind from the sails of Democrats who are counting on their own investigations to yield politically damning new discoveries about Trump.
If Mueller validates Democrats' impression that their questions remain unanswered, that will further bolster — in their eyes — the case for surfacing Trump's taxes, financial statements, business records and other documents.
Debriefing the sphinx
One trick may be in getting Mueller to say much of anything, let alone reveal new information.
He is not enthusiastic about testifying and has said he won't go beyond the contents of his written report. Prying information out of the taciturn former G-man could be a challenge for members of Congress in both parties.
But the milestone that Mueller's hearings represent is also politically vital for both parties.
For example, people who have worked for Trump have described what they called questionable practices from before Trump entered politics, including under- or over-reporting income information to banks and authorities to gain an advantage in real estate dealings.
If Democrats' investigations could substantiate that, House Speaker Nancy Pelosi, D-Calif., and the party's 2020 nominee could try to weaponize it against Trump.
The president and Republicans argue that Democrats want to redo the Russia investigation because it didn't result in findings helpful to them, and that all the subsequent investigations are pure fishing expeditions.
The White House has been fighting many of Congress' investigations by resisting committee subpoenas for witness testimony and documents. Republicans in 2020 will likely continue to paint Democrats as overzealous and focused on the wrong issues
Some of the most anti-Trump Democrats in the House — and still more of the most anti-Trump Americans around the country — believe Mueller's findings compel the House to pursue impeachment.
Pelosi doesn't agree, mindful of the need for Democrats to try to appeal to a broader swath of voters in 2020 to protect her majority and try to unseat Trump.
Republicans, with their control of the Senate, could protect Trump if Democrats in the House were to impeach him.
In fact, Trump and supporters have sometimes seemed to goad their opponents in the House to proceed with impeachment, confident the effort would ultimately fail to oust the president. A fizzled attempt would amount to another inoculation for Trump, in this view, and a rebuke to Pelosi.
These are the positions on the battlefield as Mueller enters. Will his appearance on Wednesday alter them?
Many Americans — and many members of Congress — have not read his written report. One reason why House Judiciary Committee Chairman Jerry Nadler, D-N.Y., wants Mueller to appear is simply for there to be video of the former special counsel discussing his findings.
Nadler and Democrats hope that will reach more people than the report did.
The last time Mueller appeared, for a brief statement at the Justice Department, it moved the needle for some Democrats in terms of their calls for impeachment.
So another question raised by the hours' worth of open testimony scheduled for Wednesday is whether the former special counsel's appearance will change the minds of any more members of Congress in ways his written words did not.
If Mueller's testimony results in the status quo here, too, Democrats may decide to join Republicans in finally closing the curtain on the Russia imbroglio.
The topic was not a major focus for the party's many candidates at their first debate last month, and even when they were asked about it directly, some deflected to what they called more appropriate priorities.
Former Maryland Rep. John Delaney, for example, said that although he'd be open to a prosecution against Trump after he's out of office, most voters don't have Russia on their radar screen.
"One thing, when you are out doing as much campaigning as I have done — 400 events in all 99 counties in Iowa — this is not the No. 1 issue the American people ask us about," he said. "It's not. They want to know what we're going to do for health care, how we are going to lower pharmaceutical prices, how we are going to build infrastructure, what we are going to do to create jobs in their communities."