WASHINGTON — The special counsel's investigation didn't find enough evidence to establish collusion between the Trump campaign and Russia, the Department of Justice says, but stopped short of exonerating President Donald Trump of obstruction of justice.

The conclusions of the special counsel's two-year-long investigation into possible Russian interference in the U.S. elections process were sent in a four-page letter Sunday from Attorney General William Barr to Congress.

"The cloud hanging over President Trump has been removed," said Senate Judiciary Committee Chairman Lindsey Graham, a close Trump ally.

Barr's letter says, in part, "The special counsel's investigation did not find that the Trump campaign or anyone associated with it conspired or coordinated with Russia in its efforts to influence the 2016 U.S. Presidential Election."

Mueller essentially punted on the question of obstruction of justice. Barr's summary letter says Mueller presented evidence on both sides — leaving it to the attorney general to decide. Barr told lawmakers he has concluded no obstruction of justice charges will be brought.

But the letter also states: "The Special Counsel states that 'while this report does not conclude that the President committed a crime, it also does not exonerate him.' "

"The Special Counsel did not find any collusion and did not find any obstruction. AG Barr and DAG Rosenstein further determined there was no obstruction. The findings of the Department of Justice are a total and complete exoneration of the President of the United States," White House Press Secretary Sarah Sanders said in a tweet.

President Donald Trump had been conspicuously low-key on Twitter since Friday, when Robert Mueller's investigation officially came to a close as he delivered his long-awaited findings to Barr. Trump has repeatedly called Mueller's investigation a "witch hunt."

After the release of Barr's summary letter, he quickly broke his Twitter silence, saying he feels vindicated:

Mueller's team issued more than 2,800 subpoenas and conducted more than 500 search warrants and witness interviews over the two-year investigation.

Democrats have demanded that the investigation's findings be released to the public in full, though it's still unclear whether that will happen. Among them, New Jersey Sen. Cory Booker said Sunday that the public "deserves the full report and findings... not just the in-house summary from a Trump Administration official.''

Republican Sen. Marco Rubio of Florida said Sunday that he wants all of the Mueller report to be released, including the founding documents.

Rubio appeared on NBC's "Meet the Press," echoing the call from Democrats for transparency, even going one step further. He wants to see what information was the basis for the probe and the FBI’s "extraordinary use of government surveillance power."

"Let's see all of that and put all of that out there so we can pass judgment about how the investigation was conducted, or at least the predicate for the investigation was conducted, during the Obama years," said Rubio, a member of the Senate Intelligence Committee, which is also investigating Russian interference.

Barr has said he intends to release as much as possible from the full report, though he said secret grand jury material and content related to ongoing investigations could be redacted.

Former federal prosecutor Dan Eckhart, who runs an Orlando law firm, said he's not surprised by the findings.

"You had some of the best prosecutors that are assembled in one place, and they don’t mention how many FBI agents on the case, might be hundreds, so I personally am confident with the findings," Eckhart said.

The special counsel's investigation led to charges against more than three dozen people, including six from Trump's inner circle. Paul Manafort, Michael Flynn, George Papadopoulos, and Michael Cohen all have admitted to lying or pleaded guilty to accusations.

The special counsel's office indicted more than two dozen Russians and three Russian entities last year, accusing them of hacking communications in an effort to interfere in the 2016 election.

Mueller declined to recommend further indictments in his probe.

But John S. Martin Jr., a former federal judge in the Southern District of New York, says not to rule out more indictments from elsewhere.

"The fact that there are no further indictments coming from him (Mueller) doesn't mean that there won't be any more indictments. During the course of his investigation, he has turned over certain matters to other U.S. Attorney's Offices, particularly the U.S. Attorney's Office for the Southern district of New York.

"Remember President Trump lived in New York, conducted his business in New York, ran his campaign from New York, and returned to New York almost every night. So the Southern District of New York is the place that has the broadest jurisdiction of any criminal activity committed by the president, or any of the people in his campaign, or any of his family members," Martin said.

"Aside from this investigation, it doesn’t mean that there are not other tentacles to this investigation that are ongoing," Eckhart, the former prosecutor, said. "This specifically talks about President Trump and some of his staff members responsible for getting him elected. I am sure there are other prosecutions out there," he said.

The chairman of the House Judiciary Committee, Democratic Rep. Jerry Nadler, said he would call Barr to testify on the investigation "in the near future."

Eckart said it could take months to disclose more details relating the Mueller report.

Information from the Associated Press and CNN was used in this article.