Analysis by Ronald Brownstein

(CNN) -- The results of special counsel Robert Mueller's investigation, even in the brief summary released by Attorney General William Barr, vastly reduce the legal risks to President Donald Trump while raising the political stakes in the 2020 election.

Even as Mueller left open questions about possible obstruction of justice, his report that the investigation "did not establish" coordination between the Trump campaign and Russia's interference in the 2016 election virtually ensures that voters in 2020 -- not any legal process before then -- will deliver the decisive verdict on Trump's tumultuous presidency.

And that may be the rare development both parties can welcome.

"The best thing to happen -- for the country, for the GOP, for the Democratic Party -- is for voters to resolve all these matters," says Pete Wehner, a senior fellow at the conservative Ethics and Public Policy Center and a leading Trump critic on the right. "That's how these things should be decided in a republic, absent the most extraordinary circumstances. Taking things like this out of the hands of voters usually has bad consequences all the way around."

While many grass-roots Democratic activists hoped that Mueller's investigation might force Trump from office, either through resignation or impeachment and conviction in the Senate, few Democratic political professionals ever shared that anticipation. And many believe the party will be better off running against Trump in 2020 than facing Vice President Mike Pence or another Republican, who could claim that Trump had been unfairly forced from office.

Having Trump on the ballot "is better electorally and better for having a defining election that creates a mandate, gives you a shot at (recapturing) the Senate and forces the Republican Party to rethink its direction," says veteran Democratic pollster Stanley B. Greenberg.

Trump will likely face more legal questions as additional information from the Mueller report emerges in the days and weeks ahead. House Democrats will closely examine Barr's determination that Mueller's findings did not justify a charge of obstruction of justice against the President, especially given the hint in Barr's letter that the counsel uncovered evidence on that front that the public has not yet seen. (Barr noted that Mueller's report examined actions by the President "most of which have been the subject of public reporting.")

Democrats will also closely probe the evidence behind the rare sentence from the Mueller report that Barr directly quoted: Mueller's conclusion that the investigation "did not establish that members of the Trump Campaign conspired or coordinated with the Russian government in its election interference activities."

And Trump still faces other legal challenges, headlined by the Southern District of New York indictment of his former fixer Michael Cohen, who essentially identified the President as an unindicted co-conspirator in a scheme to evade campaign finance laws by paying hush money to women who claimed extramarital affairs with him. Trump has denied having affairs with the women.

But with senior House Democrats already skeptical about impeaching Trump, that prospect has grown even more remote after Mueller's investigation concluded without any indictments alleging links between campaign officials and the Russian interference. And that means Trump's opponents will almost certainly need to defeat him at the ballot box, rather than counting on any legal intervention to short-circuit his presidency.

David Plouffe, a chief strategist for Barack Obama's campaigns, underscored that point in a tweet on Sunday that referenced the need for Democrats to build toward winning the 270 Electoral College votes required to capture the White House. "270 on 11/03/20 was always the only real route to making this a 4 and not 8 year nightmare," Plouffe tweeted. "He's not resigning, he's not getting impeached and the popular vote is not getting established."

Impacts on 2020 campaign, Democrats

While the end of the Mueller investigation unequivocally heightens the primacy of the 2020 election, the report's impact on the outcome could be more complex.

While Trump may receive a short-term bump in public support from the investigation's end, most observers in both parties expect that his approval rating will revert to the 40% to 45% range in which it generally has resided throughout his presidency.

"I think the Mueller report will be fascinating because of its substance, but in terms of public opinion, it will simply reinforce existing views on both sides," says GOP pollster Whit Ayres.

The investigation's end without further indictment is certain to embolden Trump to intensify his attacks on the media and the "deep state" that he has portrayed as conspiring against him. That could have crosscutting impacts.

On the one hand, Mueller's decisions are likely to further energize Trump's base. The President's core supporters were already likely to turn out in large numbers next year to support him. Now that turnout could rise even higher, as Trump portrays the investigation as an attempt by a contemptuous elite to not only undermine him but to silence his coalition.

But Trump's renewed confidence also seems likely to lead him toward more of the belligerent and volatile behavior that has alienated so many voters, particularly in white-collar suburbs, who are otherwise content with the economy's direction.

"I think that can cut both ways," says Democratic pollster Andrew Baumann. "I do think that this may cause some of those suburban swing voters to give him a little more leeway here, though I don't think it will be a lot, and knowing Trump he's likely to overstep and end up reinforcing the existing concerns about his temperament. So it could actually end up boomeranging and hurting him with those college-educated suburban swing voters."

Among Democrats, the Mueller report weakens the hand of the vanguard liberals pushing the party to move quickly to impeach Trump. That will reassure the party leaders and strategists who have long considered impeachment a dead end since there has never been a realistic prospect of enough Republican senators voting to remove him from office.

"If you go through the impeachment process without Republican support, then the (Senate) trial would have been his re-election campaign," says Greenberg.

But Mueller's conclusion -- absent the eventual release of significantly more damaging information in the underlying report -- also could diminish Democrats' ability to hurt Trump with the investigations they have launched in the House. The President will now have a precedent he can point to in dismissing all future investigations as another kind of "witch hunt."

"The bigger danger may be what this does towards perceptions of Democratic oversight," says Baumann. "There's plenty of room to continue proper oversight. But I think this likely means that Democrats need to be even more careful to find the right balance."

Challenge for 'never Trumpers'

The conclusion of the Mueller investigation also heightens the challenge facing the thin band of "never-Trump" GOP intellectuals and political strategists who consider his redefinition of the party around his racially barbed economic nationalism both a betrayal of conservative ideals and an electorally unsustainable course in an inexorably diversifying nation.

The easing of Trump's potential legal vulnerability strips these internal critics of a lever they hoped might loosen the President's hold on the party before 2020. But most of them have also long believed that they have a better chance of convincing the party that Trump's approach represents a dead end if it is repudiated by voters in 2020, rather than if he's somehow forced from office before then.

"The only way Trump's grip on the GOP will be loosened is if Republicans come to believe that he's toxic for their party and is undermining their electoral success," said Wehner. "It's much better for voters to decide that rather than prosecutors."

Ayres, the GOP pollster, largely agrees. He worries that Trump's strategy of squeezing bigger advantages out of groups that are shrinking in the electorate -- whites who lack college degrees, live outside of major metropolitan areas or identify as evangelical Christians -- is not "a viable electoral coalition in the long run" as those groups steadily decline. But he says Republicans are far more likely to question Trump's direction if he loses in 2020 than if he is removed through other means -- or for that matter, if he wins a second term.

"How the Trump era ends will have a dramatic effect on what the Republican Party looks like going forward," Ayres says.

All these roads converge into the 2020 election. Both in style and substance, Trump has proved to be a uniquely polarizing President, the first in the history of Gallup polling never to reach 50% approval at any point this far into his presidency.

He has pursued an agenda aimed almost solely at the preferences of Republican constituencies in economics (tax cuts, deregulation and attempted repeal of the Affordable Care Act) and social issues (conservative Supreme Court justices, opposition to abortion), and through his language on immigration and other issues he has appealed to white racial resentments more openly than any national figure since George Wallace.

Trump has shattered the boundaries of presidential behavior, in language, temperament and his scornful posture toward any institution that defies him, from the courts and federal law enforcement agencies to Congress and the business community. In the process, he has thrilled a passionate band of supporters, horrified the core constituencies of the Democratic Party and sent swing suburban voters stampeding away from the GOP in the 2018 election.

The thought that all these confrontations and collisions could be resolved through a legal judgment on the turbulent man at their center was always improbable. Now it is more certain than ever that Americans themselves must decide Trump's fate.