WASHINGTON – Special counsel Robert Mueller’s investigation into Russian interference in the 2016 election might be nearing an end, but the political and legal battle over his work has barely begun.

Lawmakers from both parties plan to press for access not just to the report that is likely to mark the end of Mueller's work but also to the evidence he gathered during an investigation that spanned nearly two years and pried deeply into Donald Trump's presidential campaign and administration. The demands would almost certainly set up a battle between Congress and the Justice Department.

Mueller has indicted 34 people, including Russian intelligence operatives and some of Trump's closest aides and advisers. In doing so, he revealed a wealth of details about a sophisticated Russian effort to influence the 2016 election and about a campaign eager to reap the benefits of that activity. What he might add in a final report remains uncertain.

Lawmakers – particularly newly powerful House Democrats, who have launched a barrage of investigations into the president and made no secret of the fact that they could be the forerunners of an impeachment inquiry – are exploring ways to force the administration to turn over conclusions and evidence it might prefer to keep secret.

“We expect the full report," said Rep. Jerrold Nadler, D-N.Y., the chairman of the Judiciary Committee. "If we don’t get it, we’ll do what we have to do to get it. If that means subpoenaing it, we’ll subpoena it."

The first move belongs to Mueller's boss, Attorney General William Barr.

He must decide how much of Mueller's final report will become public. Justice Department rules say that the special counsel must give Barr a confidential report when he is done, explaining why he charged some people and not others. Barr said he will determine how much of Mueller's work Congress sees.

Any decision seems certain to provoke a fight.

Rep. Doug Collins of Georgia, the top Republican on the Judiciary Committee, said he expects Democrats will maneuver to get the report and other evidence Mueller collected, even though he thinks it will exonerate Trump.

"This is going to be a legal battle," Collins said.

House committees have begun requesting documents from the White House as part of broad inquiries into Trump and his namesake business. Lawmakers have taken testimony from Trump's former personal lawyer Michael Cohen and opened a corruption investigation by sending document requests to 81 people and organizations associated with the president, including the White House, his private business and his children.

Trump has dismissed the investigations as "presidential harassment."

House Democrats intend to intensify and expand their investigations, building on what they expect to be the relatively narrow foundation of the Mueller report about Russian election interference into a broader search for public corruption, obstruction of justice and foreign influence on U.S. policy.

"We'll certainly be bringing in any number of witnesses, some of them new, others who have been before the committee before," said Rep. Adam Schiff, D-Calif., who heads the House Intelligence Committee investigating Russian interference in the election, efforts by foreign powers to influence Trump and his financial entanglements. "We have a lot of work to do."

Republicans, who bristle at House investigations they see as fishing for reasons to impeach the president, have nonetheless embraced the idea of obtaining Mueller's conclusions. After two years of anticipation, Collins said he expects a report that will reveal no wrongdoing by Trump.

"All of a sudden, Christmas came and no present," Collins said.

The attorney general is gatekeeper

After Mueller submits his report, Barr must decide how much he can reveal to Congress or the public.

"I also believe it is very important that the public and Congress be informed of the results of the special counsel's work," Barr told senators at his confirmation hearing in January. "My goal will be to provide as much transparency as I can consistent with the law."

Barr said he would withhold classified information, grand jury information and information subject to executive privilege. How extensively those would apply to Mueller's work remains to be seen, but Barr told lawmakers he would "not tolerate an effort to withhold such information for any improper purpose, such as to cover up wrongdoing."

Barr said the Justice Department should not release "derogatory" information about people who are not charged with crimes. Its Office of Legal Counsel has taken the position that a sitting president cannot be charged. Democrats worried that the combination of those policies would justify withholding information about Trump. Barr said he wouldn’t let political interests influence his judgment.

Bruce Udolf, a former federal prosecutor and associate independent counsel during the Whitewater investigation, said he was confident Barr would release what he could.

"I would be very surprised if Barr didn't publish a good portion of whatever is prepared by Mueller," said Udolf, who is in private practice in Florida. "To the extent that he does not, I would think there would be a good reason."

One reason is that some of the information is protected by other federal laws. Mueller's investigation has made extensive use of grand juries to gather evidence, but federal law puts strict limits on the disclosure of the evidence they obtain. Some of the subjects Mueller is investigating have drawn on classified information; even the lists of subjects covered by the inquiry was classified.

"This notion that Congress is going to throw a subpoena on Bob Mueller and say, 'Box up all the grand jury stuff, and give it to me': I think that's a fantasy," said Patrick Cotter, a former federal prosecutor who is in private practice in Chicago.

Democratic lawmakers said they will have little patience with some of those arguments. The Justice Department gave the Republican majority in Congress more than 880,000 pages of documents through last June about the investigation into former Secretary of State Hillary Clinton’s email server, a case in which no one was prosecuted, Schiff noted.

"The Justice Department cannot now maintain a different policy," Schiff said.

Lawmakers eager for Mueller report

Lawmakers of both parties are eager to hear what Mueller found, either because they expect his work to exonerate the president or to implicate him.

Both of the top lawmakers on the House Intelligence Committee said it's important that Congress obtain Mueller's report.

“If he does put out a report, you’re going to see people claiming that we have to make it public. That’s fine. But I want everything that Mueller did made public,” Rep. Devin Nunes, R-Calif., the top Republican on the intelligence panel, told an audience at the Conservative Political Action Conference. “I want every email. I want everybody that they wiretapped. Every warrant that they got. Every single thing that Mueller used needs to be made public for all of America to see.”

Collins said Republicans aren't trying to release classified or grand jury evidence but rather information that illustrates Democrats are overreaching for wrongdoing that doesn't exist.

Schiff, who has clashed repeatedly with Nunes, largely agreed on releasing as much information as possible from the Mueller investigation. Schiff said the special counsel has seized so much evidence from so many people in the inner ring of Trump's political orbit – including adviser Roger Stone and former campaign chairman Paul Manafort – that the only way for Congress to see the details is to obtain them from the Justice Department.

Udolf cautioned against lawmakers wading into grand jury evidence because prosecutors should be trusted to do their jobs.

"It's likely to discredit an otherwise righteous investigation by adding a political taint that shouldn't otherwise be there," Udolf said. "People tend to view things that politicians do with a jaundiced eye."

Six House chairmen of committees wrote to Barr on Feb. 22 saying there is significant public interest in full disclosure of information “about the nature and scope of the Russian government’s efforts to undermine our democracy.”

“We write to you to express, in the strongest possible terms, our expectation that the Department of Justice will release to the public the report Special Counsel Mueller submits to you – without delay and to the maximum extent permitted by law,” the chairmen said.

Lawmakers from both parties said they counted on Mueller's office to deliver the facts and to determine whether anyone committed a crime.

“We need a thorough and a comprehensive report on the investigation so that we can know what the facts are,” said Sen. John Cornyn, R-Texas, a member of the Intelligence Committee. “He’s got a particular responsibility, which is to conduct a criminal investigation, and we have a different responsibility, which is more political in nature.”

Congress' most potent tool for obtaining that information would be a subpoena, but subpoenaing Mueller's report or his evidence could trigger a court battle with the Justice Department, which could try to persuade a judge to keep some records secret. A federal lawsuit by the House Oversight Committee to obtain documents about the department's gun-running investigation called Operation Fast and Furious lasted more than six years.

"There is certain evidence only in possession of the special counsel," Schiff said of the potential need for a subpoena. "If it is not shared, then the American public will never get the full story."

Collins, the Judiciary Republican, said the department has long fought to avoid releasing information that is classified, from a grand jury or as part of an ongoing investigation. He said prosecutors might want to keep other details secret because they are pursuing other investigations related to Trump that will continue after Mueller wraps up.

"This is historically something that DOJ has fought back on," Collins said. "They have never released this information, and we don't expect that to happen now."

Rep. Eric Swalwell, D-Calif., said there might have been cases in which Mueller couldn’t prove a crime beyond a reasonable doubt, but Congress could still take action.

“I hope at the very least, if there is any finding of wrongdoing at all, that that would go to the House Judiciary Committee,” said Swalwell, a member of the Intelligence Committee and a former Alameda County prosecutor. “If there is any intelligence gleaned from it as to how we could protect our country in the future, that it would go to the House Intelligence Committee.”

He said Congress has a responsibility to use the information to prevent meddling.

“At the end of the day, our job is to tell the American people what Russia did, how they did it, who they worked with, what the government response was and whether it was adequate," Swalwell said. "And then, learning from all of that, recommend reforms to prevent it from ever happening again.”

Investigation could leave loose ends

The legal cases Mueller's office launched could go on for months even after his investigation is concluded.

Mueller's investigation produced a web of criminal cases against a half-dozen of Trump's closest aides and advisers, many of which have yet to conclude.

As Mueller's office prepares to wind down, it has begun handing those cases over to other branches of the Justice Department, including its national security prosecutors and U.S. attorneys offices in Washington and Virginia. Prosecutors in New York could pursue cases involving the Trump Organization.

The loose ends include a criminal case filed against Stone in January accusing him of lying to Congress about his interactions with the group WikiLeaks, which prosecutors said published emails stolen by a Russian intelligence service. A passage in the Stone indictment said that after a dump of email in July 2016, "a senior Trump campaign official was directed" to contact Stone about additional releases.

Stone, who has maintained his innocence, could go on trial this year.

Prosecutors haven't resolved their cases against former national security adviser Michael Flynn and political operative Rick Gates. Both men pleaded guilty to federal charges, but their sentencing was delayed, so they could provide information to investigators.

Mueller's office is still fighting two legal challenges over its attempts to gain evidence that prosecutors said was important to their investigation.

In one, Andrew Miller, a former aide to Stone, challenged a subpoena to testify before a grand jury, arguing that the entire special counsel investigation was illegal. Two courts have rejected that argument, but Miller's lawyers have indicated they could take the challenge to the Supreme Court.

In the other, Mueller's office seeks to force an unnamed company to turn over records to a grand jury. The company, which is owned by an unidentified country, has refused to comply and faces a penalty of $50,000 a day until it turns over the records. Its challenge is pending before the Supreme Court.

More about milestones in the Mueller investigation:

Mueller's Russia investigation: Trump's legal team braces for report, hasn't talked with special counsel in 'weeks'

Michael Cohen's testimony prompts a new question: In web of Trump investigations, is anyone safe?

Robert Mueller has spent two years investigating Trump, and he hasn't said a word. It's possible he never will.

Robert Mueller: Here's what to expect in Friday's court filings on Paul Manafort and Michael Cohen

Michael Flynn re-emerges as major witness in Robert Mueller's inquiry – and at least two others