(CNN) In light of the March 27 letter that special counsel Robert Mueller sent to Attorney General William Barr, questions are swirling as to whether Barr misled Congress in testimony last month.

In his letter , Mueller expresses misgivings over how Barr characterized the findings of the special counsel report in a summary that the attorney general released on March 24. But in testimony to Congress in April, Barr said he did not know whether Mueller supported his summary's conclusion, and that he did not know the reasons behind reports that members of Mueller's team were frustrated over his summary.

Some Democratic members of Congress are now calling for Barr to resign and claim that his answers were misleading.

So did Barr mislead or even lie to Congress?

Facts first: The standard for lying to Congress and committing perjury is very high and willful intent to mislead must be proved. But if the question is whether Barr was being fully truthful and forthcoming to Congress in his answers, Mueller's letter presents problems to Barr's position to the contrary.

On April 10, in a back and forth between Barr and Sen. Chris Van Hollen over Barr's March 24 letter, the Maryland Democrat asked Barr, "Did Bob Mueller support your conclusion?"

"I don't know whether Bob Mueller supported my conclusion," Barr replied.

Even when narrowly taken, Barr's answer stretches credulity. In his letter, Mueller specifically says that Barr's summary laying out the bottom-line conclusions of the report "did not fully capture the context, nature, and substance of this Office's work and conclusions." From this, it appears Mueller was not satisfied with Barr's conclusions.

More broadly, Mueller also expressed concern that Barr's summary created "public confusion about critical aspects of the results of our investigation" which "threatens to undermine a central purpose for which the Department appointed the Special Counsel."

On Tuesday night, after news broke of the Mueller letter, Van Hollen lashed out. "We now know Mueller stated his concerns on March 27th," Van Hollen tweeted , "and that Barr totally misled me, the Congress, and the public. He must resign."

During a hearing on April 9, Congressman Charlie Crist, a Florida Democrat, asked Barr about reports that some members of Mueller's team were "frustrated at some level with the limited information" included in the AG's summary letter, specifically "that it does not adequately or accurately, necessarily, portray the report's findings. Do you know what they're referencing with that?"

"No, I don't," Barr said, before adding: "I think, I suspect, that they probably wanted more put out."

Barr's suggestion that he merely "suspect(ed)" that members of the Mueller team wanted more information put out to the public seems inaccurate -- Mueller's letter to Barr specifically requested that the AG "not delay release of" the executive summaries of the report.

During his hearing to the Senate Judiciary Committee on Wednesday morning, Sen. Patrick Leahy, a Vermont Democrat, asked Barr about his comments to Crist. "Why did you testify on April 9 that you didn't know the concerns being expressed by Mueller's team? When, in fact, you had heard those concerns directly from Mr. Mueller two weeks before."

In his response, Barr said that he had spoken with Mueller about the special counsel's March 27 letter. "I talked directly to Bob Mueller about his letter to me and specifically asked him, 'What exactly are your concerns? Are you saying that the March 24 letter was misleading or inaccurate, or what?' He indicated that it was not. He was not saying that."

Barr continued by noting that he did not "know what members (Crist is) talking about and I certainly am not aware of any challenge to the accuracy of the findings."

Again, Barr can be seen as splitting hairs here, especially given that Crist noted that concerns within the special counsel's office were not just about the accuracy of Barr's summaries, but in how adequately he had portrayed the work of the special counsel.

To clearly state that he did not know what these reports were referencing, as he did to Crist on April 9, while perhaps not rising to the level of an outright lie, is clearly an example of Barr not being completely forthcoming about what he knew at the time of his testimony.

"For testimony to be legally actionable as a lie," CNN legal analyst Michael Zeldin said, "it has to meet a pretty precise standard."

Zeldin adds that while Barr was less than fully forthcoming that Mueller had written a letter complaining about the situation, "I still think you would have a very difficult time trying to build a criminal case on the basis of the Crist/Barr Q&A."