Attorney General William Barr criticized special counsel Robert Mueller on Wednesday for refusing to make a decision about whether his Russia investigation showed that President Donald Trump committed an obstruction of justice offense.

In his first public testimony since the release of a redacted version of the Mueller report, Barr repeatedly delved into semantic squabbles with the panel's Democratic minority, intensifying Democrats' calls for Mueller himself to testify and leading some of them to accuse Barr of being deliberately misleading.

During the Senate Judiciary Committee hearing Wednesday morning, Barr said that he believed the special counsel should have stated whether his 22-month probe found enough evidence to show whether Trump had committed an obstruction crime.

"I think if he felt that he should not go down the path of making a traditional prosecutive decision, then he should not have investigated," Barr said.

"That was the time to pull up."

Barr told Sen. Chuck Grassley, R-Iowa, that he and Deputy Attorney General Rod Rosenstein both believe it was Mueller's responsibility to come to a decision on obstruction — "not just charging, but to determine whether or not the conduct was criminal," Barr said, adding that "the president could not be charged as long as he was in office."

Barr said he was "not really sure of" Mueller's reasoning on the issue. But the Russia report notes that the Justice Department's Office of Legal Counsel, or OLC, has set a precedent against indicting a sitting president. "This Office accepted OLC's legal conclusion for purposes of exercising prosecutorial jurisdiction," Mueller wrote in the report.

The Justice Department declined to comment beyond Barr's remarks. A spokesman for the special counsel declined to comment.

The attorney general also questioned why Mueller investigated numerous instances of potential obstruction if he ultimately was not going to make a decision.

"The other thing that was confusing to me was that the investigation carried out for a while as additional episodes were looked into, episodes involving the president," Barr said during questioning from Sen. Lindsey Graham, R-S.C. "So my question is or was why were those investigated if at the end of the day you weren't going to reach a decision on them?"

Hours before Barr was set to face the lawmakers, news outlets reported that Mueller, in late March, sent a letter to Barr complaining about the attorney general's initial four-page summary of the 448-page Russia report's principal conclusions.

Barr, in that summary to congressional Judiciary committee leaders, said that the Mueller report found that neither Trump nor anyone associated with his 2016 campaign coordinated with the Kremlin. Barr also wrote that while Mueller's report "does not exonerate" Trump on the question of whether he obstructed justice, Barr and Deputy Attorney General Rod Rosenstein determined that the evidence was "not sufficient" to establish an obstruction offense.

Mueller told Barr in the reported letter that the attorney general's summary "did not fully capture the context, nature, and substance" of the full report.

"There is now public confusion about critical aspects of the results of our investigation," Mueller continued. "This threatens to undermine a central purpose for which the Department appointed the Special Counsel: to assure full public confidence in the outcome of the investigations."

In his testimony, Barr said that after receiving Mueller's complaint, the special counsel told him in a phone call that he was actually frustrated with the way the media had covered Barr's letter.

"He was very clear with me that he was not suggesting that we had misrepresented his report," Barr said in his opening statement.

Barr's testimony only heightened Democrats' calls for Mueller to come before Congress and explain the report in his own words.

"I think it's no wonder special counsel Mueller thought your four-page letter created public confusion about critical aspects of the results of the investigation and that that threatened to undermine the central purpose for which he was appointed," said Sen. Chris Coons, D-Del. "I think we need to hear from special counsel Mueller."

Sen. Amy Klobuchar, D-Minn., who is running for president in the 2020 election, told reporters during a midday break in the hearing that "you just see this repeated pattern of misleading, and you know, [Barr's] job should be to get the truth out."

Sen. Mazie Hirono, D-Hawaii, was more blunt.

"You lied to Congress," Hirono told Barr in the hearing. "You should resign."

Read Mueller's letter to the attorney general: