WASHINGTON (AP) — Special counsel Robert Mueller on Friday turned over his long-awaited final report on the contentious Russia investigation that has cast a dark shadow over Donald Trump's presidency, entangled Trump's family and resulted in criminal charges against some of the president's closest associates.

The report, still confidential, marks the end of Mueller's probe but sets the stage for big public fights to come. The next steps are up to Trump's attorney general, to Congress and, in all likelihood, federal courts.

The Justice Department said Mueller delivered his final report to Attorney General William Barr and officially concluded his probe of Russian election interference and possible coordination with Trump associates. The report will now be reviewed by Barr, who has said he will write his own account communicating Mueller's findings to Congress and the American public.

Barr said he could release his account to Congress as soon as this weekend.

With no details released at this point, it's not known whether Mueller's report answers the core questions of his investigation: Did Trump's campaign collude with the Kremlin to sway the 2016 presidential election in favor of the celebrity businessman? Also, did Trump take steps later, including by firing his FBI director, to obstruct the probe?

But the delivery of the report does mean the investigation has concluded without any public charges of a criminal conspiracy between the campaign and Russia, or of obstruction by the president.

It's unclear what steps Mueller will take if he uncovered what he believes to be criminal wrongdoing by Trump, in light of Justice Department legal opinions that have held that sitting presidents may not be indicted.

U.S. Sen. Chris Murphy, D-Conn., quickly released the following statement on Friday after Mueller presented Barr with the report from his nearly two-year-old investigation into Russian interference in the 2016 presidential election and potential ties to the Trump campaign, as well as possible obstruction of justice.

"Attorney General Barr should immediately turn over all records to Congress and make the full Special Counsel's report public. Mueller investigated issues at the very core of our democracy — including whether a foreign power worked with the president or his campaign to get him elected, and whether Trump and those around him tried to cover it up. The American people deserve to know all the facts now. The future of American democracy depends on it," said Murphy.

U.S. Rep. Joe Courtney, D-2nd, and Sen. Richard Blumenthal, D-Conn., also followed suit shortly afterward.

"The country needs full and complete transparency on alleged interference in our elections, and I once again call for the report to be made public in its entirety," Courtney said. "Just last week, the House of Representatives voted in overwhelming bipartisan fashion to pass a resolution by a vote of 420-0 that expressed this same sentiment – that the report should be made available to Congress and to the public once completed. The report is now completed. The Department of Justice needs to fulfill its duty to the American people and make public the findings of the Mueller Investigation."

"Now that the Special Counsel's report has been delivered to the Attorney General, the imperative for transparency and full disclosure is immediate and urgent," Blumenthal said. "The public has a right to know all of the findings and evidence that resulted from this investigation. The public interest is paramount in disclosing not only conclusions, but the facts that led to them. There is no excuse for concealing any part of this report along with its findings and evidence – it would be tantamount to a cover-up."