WASHINGTON (Reuters) - Now that Special Counsel Robert Mueller has submitted the report on his investigation of Russia’s role in the 2016 U.S. election, Attorney General William Barr must decide how much of the document - if any - to make public.

FILE PHOTO: Robert Mueller, as FBI director, testifies before a House Judiciary Committee hearing on Federal Bureau of Investigation oversight on Capitol Hill in Washington June 13, 2013. REUTERS/Yuri Gripas

Justice Department regulations governing special counsels adopted in 1999 give Barr, the top U.S. law enforcement official, broad discretion in deciding how much to release to Congress and the public. Barr, in his January Senate confirmation hearings after being nominated by Trump, promised to “provide as much transparency as I can consistent with the law” - a pledge that still gives him a lot of wiggle room.

Trump said on Wednesday he does not mind if the public is allowed to see the report.

Mueller was named special counsel in May 2017 by the department’s No. 2 official, Rod Rosenstein, to take over an investigation that had been headed by the Federal Bureau of Investigation. He examined whether Trump’s 2016 campaign conspired with Russia and whether the president unlawfully sought to obstruct the probe. Trump has denied collusion and obstruction and Russia has denied election interference.

Here is an explanation of the rules Barr must follow and the political pressures that he faces in deciding on disclosure of Mueller’s findings.

WHAT DO JUSTICE DEPARTMENT REGULATIONS CALL FOR?

Justice Department regulations do not require the release of the entire special counsel report but also do not prevent Barr from doing so, giving him leeway to disclose it if it is in the public interest.

Special counsels can be appointed by the department to investigate matters of high sensitivity that are not handled through the normal channels.

The department placed limits on special counsel powers in the 1999 regulations creating the post.

The regulations state that when an investigation is conducted a special counsel must provide the attorney general a “confidential report” explaining why particular individuals were or were not charged.

The regulations require Barr to notify the top Republicans and Democrats on the House of Representatives and Senate Judiciary Committees that the investigation has ended. Department policy calls for Barr to summarize the confidential report for Congress with “an outline of the actions and the reasons for them.” According to the regulations, Barr “may determine that public release of these reports would be in the public interest, to the extent that release would comply with applicable legal restrictions.”

In deciding what to release, Barr may have to confront thorny legal issues involving secrecy of grand jury testimony, protecting classified information, communications with the White House possibly subject to the principle of executive privilege shielding certain information from disclosure, and safeguarding confidential reasons for why some individuals were not charged.

WHAT POLITICAL PRESSURE MIGHT BARR BE FEELING?

Some Democrats have expressed concern Barr may try to shield Trump and bury parts of the report. Barr may feel pressure from the Republican president to conceal damaging parts of Mueller’s report and release any findings that may exonerate him.

Barr, 68, is a veteran Washington insider who also was attorney general from 1991 to 1993 under Republican President George H.W. Bush. He has embraced an expansive view of presidential powers but also is considered a defender of the rule of law.

Trump fired Barr’s predecessor, Jeff Sessions, in November after complaining for months about Sessions’ 2017 decision to recuse himself from overseeing the Russia investigation.

WHAT IF BARR DECLINES TO RELEASE THE FULL REPORT?

Democrats control the House and some already have pledged to subpoena the report and Mueller and go to court if necessary to secure its full release. The House on March 14 voted 420-0, with four conservative Republican lawmakers voting “present,” to approve a non-binding resolution urging Barr to make public everything in Mueller’s report that is not expressly prohibited by law and to provide the entire document to Congress.

HOW HAVE OTHER SPECIAL COUNSEL REPORTS BEEN HANDLED?

Only two special counsels have been appointed under the 1999 regulations: Mueller and former Senator John Danforth, who was appointed that same year to investigate the deadly 1993 federal raid on the Branch Davidian cult compound in Waco, Texas. Danforth’s report in 2000 cleared government officials of wrongdoing.

In appointing Danforth, Attorney General Janet Reno specifically directed him to draft a report for public release on his findings, which he did. Rosenstein made no such demand on Mueller.