The conclusion by the special counsel that President Trump did not conspire with Russia all but assures that Mr. Trump’s political fate will be determined at the ballot box next year — intensifying pressure on Democrats to settle on a candidate and a policy agenda that offers them the best chance to defeat the president.

With House Democrats now far less likely to impeach Mr. Trump, and Senate Republicans certain to resist removing him if they did, the 2020 race will revolve more around his performance in office than how he won in the first place.

That may disappoint some Democrats, who believe that the Russian interference on Mr. Trump’s behalf in the 2016 race makes his presidency illegitimate. But it offers the party a chance to oust him through democratic means that would be harder to dispute, rather than the divisive tactic of impeachment.

So far, the response of most of the candidates to the Mueller report has been to demand that Attorney General William P. Barr release the document in full. But some top Democrats are urging them to move past the report and instead focus on the promises they say he has failed to keep, and highlight their differences with the president on issues like immigration, tax policy and health care.