Hovering above the report fallout is the question of impeachment, and the party is divided.
Presidential candidate Senator Elizabeth Warren called for impeachment hearings into Trump's conduct, saying elected leaders should "do their constitutional duty".
The party's leaders in Congress instead want to hold committee hearings to probe the evidence. House Judiciary committee chairman Jerrold Nadler said: "The idea is not to debate articles of impeachment," but rather to get all the facts and "then decide what to do about it".
The practicalities of impeachment in a divided Congress are daunting for the Democrats.
The Democratic-controlled House of Representatives could begin impeachment proceedings, but the Republican-controlled Senate would have the final say on whether to remove Trump from office with two-thirds approval required. In the current harshly partisan climate, impeachment would almost certainly fail.
Polls show impeachment is unpopular with most Americans, although the positions could shift. In last November's Midterm elections, voters opposed it by 56 to 39 per cent in the exit poll. A poll last month put it at 54 to 42 per cent.
Mueller found that Russia interfered in the 2016 presidential election in a "sweeping and systematic fashion". Despite also finding extensive links between Russian officials and members of the Trump campaign, he did not find that Trump's campaign illegally conspired with Russia.
On the issue of Trump possibly obstructing justice, Mueller declined to charge Trump because of the legal convention that a sitting US president cannot be indicted. Mueller wrote: "While this report does not conclude that the President committed a crime, it also does not exonerate him".
Mueller looked at 10 instances of possible obstruction by Trump. "The President's efforts to influence the investigation were mostly unsuccessful, but that is largely because the persons who surround the President declined to carry out orders or accede to his requests."
Trump responded to the report's release with a tweet in Game of Thrones-style fonts saying: "Game over". In Game of Thrones terms, impeachment would be a Ned Stark play: The "honourable" approach from a Democratic viewpoint, but potentially costly.
Warren argued in a tweet: "To ignore a President's repeated efforts to obstruct an investigation into his own disloyal behaviour would inflict great and lasting damage on this country, and it would suggest that both the current and future presidents would be free to abuse their power in similar ways."
But impeachment hearings would allow Trump to turbo-rally Republicans in a way that committee hearings, with far less at stake, would not. And failing at the end - possibly as voting in the 2020 primaries is underway - would allow Trump to loudly claim vindication.
In 2020, Trump will face the electorate's verdict. That's the one that counts.
