In this weekly column "Cross-exam," Elie Honig, a former federal and state prosecutor and CNN legal analyst, gives his take on the latest legal news and answers questions from readers. Post your questions below. The views expressed in this commentary are his own. View more opinion articles on CNN. Watch Honig answer reader questions on "CNN Newsroom" at 5:40 p.m. ET Sundays.

(CNN) Any trial lawyer knows that it is one thing to read a witness statement, but quite another to see the witness testify live. Live testimony is the ultimate moment of truth. Prosecutors spend hours preparing a key witness, reviewing statements and doing dry runs. But when the witness raises his or her hand and gets sworn in, the stakes multiply.

The American public will soon have the opportunity to hear live testimony from a witness who could turn out to be the most important of all: Don McGahn, former White House counsel to President Donald Trump.

After the release of special counsel Robert Mueller's redacted report , Rep. Jerrold Nadler, chairman of the House Judiciary Committee, issued a subpoena to McGahn. From a prosecutor's perspective, McGahn is perfectly situated to be a star witness. He has the two things that can move the opinion of the fact-finder, whether a trial jury or the American public: access and credibility.

McGahn served as Trump's White House counsel for nearly 21 months, from Trump's first day in office until October 2018. In that capacity, he had firsthand access to the most important conversations in the administration. And McGahn has long been respected across the political aisle. Not even Trump -- who was reportedly unsettled at McGahn's cooperation with Mueller, though Trump claimed he "allowed" McGahn to testify -- has turned on McGahn and questioned his credibility (not yet, at least).

McGahn's testimony, as summarized in Mueller's report , is potentially devastating to Trump on the matter of obstruction of justice. According to Mueller, in March 2017, Trump told McGahn to prevent then-Attorney General Jeff Sessions from recusing himself from the Russia investigation; Trump "expressed anger at the decision and told advisers that he should have an attorney general who would protect him." McGahn later advised Trump not to have contact with FBI Director James Comey and others at the Department of Justice about the Russia probe.

Most sensationally, in June 2017, when the media reported that Mueller had begun to investigate obstruction of justice, Trump called McGahn at home and directed him to have Deputy Attorney General Rod Rosenstein fire Mueller. McGahn did not carry out Trump's order, "deciding that he would resign rather than trigger what he regarded as a potential Saturday Night Massacre." Compounding the matter, in early 2018, when the media reported on Trump's attempt to have McGahn fire Mueller, Trump pressured McGahn -- indirectly, through other White House officials, and directly, in the Oval Office -- to falsely deny the media reports. McGahn refused.

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Apparently recognizing the potentially devastating impact of McGahn's testimony, the White House reportedly may assert executive privilege in an effort to block it. But executive privilege -- the notion that certain communications between the President and his advisers should remain confidential -- seems inapplicable here. First, under the legal " crime-fraud exception ," testimonial privileges do not apply to conversations that occurred in the course of committing a crime -- here, at least arguably, obstruction. Second, the White House likely has given up, or "waived," the privilege by permitting McGahn to speak to Mueller about the communications and then by allowing McGahn's testimony to not be redacted in the final report. Typically, once a privilege is waived, it cannot then be un-waived later.

Some witnesses shine on the witness stand, exuding calm, consistency and credibility, while others flop, equivocating or recanting their prior statements. In just a few weeks, we should see McGahn testify in his own words. If McGahn flops, Trump can breathe a sigh of relief. But if he backs up his statements to Mueller with forceful, persuasive live testimony, then he could galvanize public opinion and increase pressure on Congress to take further action.

Now, your questions:

Niranjan, Connecticut: Does the Mueller report state that the attorney general should make the determination regarding obstruction of justice, or does it refer the report to Congress to make the determination?

Before we saw the Mueller report, Attorney General William Barr told us two important things about obstruction -- both of which turned out to be misleading at best.

First, Barr wrote in his four-page letter purporting to summarize Mueller's "principal conclusions" that Mueller "did not draw a conclusion one way or the other as to whether the examined conduct constituted obstruction." This, according to Barr, "leaves it to the attorney general to determine whether the conduct described in the report constitutes a crime." Predictably -- given his unsolicited 2018 memo to the Justice Department excoriating Mueller's obstruction theory as "fatally misconceived" -- Barr declared that Mueller's findings did not support an obstruction charge against Trump.

But, in the report , Mueller never actually "leaves it to" Barr to decide obstruction. To the contrary, Mueller seems to look to Congress to resolve the obstruction issue: "the conclusion that Congress may apply the obstruction laws to the President's corrupt exercise of the powers of the office accords with our constitutional system of checks and balances and accords with the principle that no person is above the law." Mueller here appears to call on Congress to take up the issue of Trump's obstruction.

Second, Barr stated at his press conference before the report's release that Mueller's decision not to make a traditional prosecutorial judgment on obstruction was based on the facts of the case, not on the Justice Department policy memo advising against indictment of a sitting president. This mirrored Barr's claim in his four-page letter that Mueller declined to decide obstruction because of "difficult issues of law and fact."

In the report, however, Mueller makes clear that the Justice Department policy was, in his view, the primary obstacle to an obstruction charge. Mueller notes that in light of the policy, "we determined not to apply an approach that could potentially result in a judgment that the President committed crimes." Then, in a passage that reads like a devastating closing argument at a jury trial, Mueller lays out 11 potentially obstructive acts by Trump. Mueller concludes as follows: "if we had confidence after a thorough investigation of the facts that the President did not commit obstruction of justice, we would so state. Based on the facts and applicable legal standards, we are unable to reach that judgment." In other words: If we found that Trump did not commit obstruction, we'd say so -- and we're not saying so.

Despite his unilateral proclamation that Trump did not commit obstruction, Barr has technically done nothing to limit Congress' ability to take the matter up for further proceedings, including impeachment. A determination of criminality is entirely separate from impeachment . President Bill Clinton was impeached, for example, without any criminal charges filed against him. Congress remains well within its rights to say, effectively: thanks for your opinion, Mr. Attorney General, now we will do our job and consider whether impeachment is warranted.

That said, Barr undoubtedly did Trump a major political favor. By announcing his view that obstruction charges were unwarranted, and by giving the public a slanted view of Mueller's findings, Barr set the initial "no obstruction" narrative and let it calcify the public perception for nearly a month before Mueller's report came out.

Evi, Canada: Doesn't asking White House staff to execute actions that constitute obstruction prove Trump's intention to obstruct justice?

The Mueller report lays out a devastating timeline of obstructive acts by Trump. I've charged and convicted defendants on obstruction and perjury charges with a fraction of what Mueller alleges against the President. In one case, for example, I charged, tried and convicted a defendant who told his girlfriend to leave town until his trial was over (she didn't). Compare that to the President's ongoing campaign over more than a year to shut down the Mueller investigation, including firing the FBI director, pressuring the attorney general, trying to fire the special counsel, lying to the public and instructing subordinates to lie.

Luckily for Trump, in some of those instances, his subordinates defied or ignored his commands. For example, FBI Director James Comey refused to shut down the investigation of former national security adviser Michael Flynn, White House counsel Don McGahn did not follow up on Trump's instructions to have Mueller fired, and former campaign manager Corey Lewandowski did not send a message intended to cause Attorney General Jeff Sessions to take control of and limit the ongoing inquiry. Mueller notes in the report that Trump's "efforts to influence the investigation were mostly unsuccessful, but that is largely because the persons who surrounded the President declined to carry out orders or accede to his requests."

Under the law, however, an attempt is a crime even if the criminal act had not been completed. The federal obstruction of justice statute explicitly applies to anyone who "obstructs, influences, or impedes any official proceeding, or attempts to do so." Sure, attempts may not cause the same societal harm as completed crimes, but the offender's intent is no different: A bad shooter who misses his target had the same intentions as a good shot who hit it squarely. Comey, McGahn, Lewandowski and others did the right thing by ignoring or defying the President's corrupt orders, but their refusals should have little to no bearing on the President' ultimate culpability.

Greg, California: Why can the President not be indicted -- if there is no law that explicitly says that?

The notion that a sitting president cannot be indicted is not embedded in the Constitution, statute or judicial ruling. It is an internal Justice Department policy , imposed by the department on itself.

This policy goes back decades. It was adopted in 1973 (in the wake of President Richard Nixon's resignation while under investigation), and it was updated and reaffirmed in 2000 (shortly after the impeachment of President Bill Clinton). The primary justification for the policy is that indictment of the sitting president could effectively cripple the executive branch: "To wound (the President) by a criminal proceeding is to hamstring the operation of the whole governmental apparatus, both in foreign and domestic affairs."

But Justice Department policies come and go -- at the attorney general's discretion. There is nothing preventing any attorney general from revising or rescinding any such internal policy. In my time with the Justice Department, from 2004 through 2012, attorneys general routinely made significant policy changes. For example, in 2010, Attorney General Eric Holder issued a new policy giving federal prosecutors more discretion to exercise leniency in charging, plea and sentencing decisions. This replaced a stricter policy issued by Attorney General John Ashcroft.

The Justice Department policy may have saved Trump from indictment here, but it likely will become a political issue heading into the 2020 election. Expect every candidate -- including Trump -- to be asked: "If elected, will you rescind the existing policy against indicting a sitting president?"

Dennis, Colorado: If a president commits a murder, would the Justice Department indict him?

No. The policy against indictment of a sitting president makes no exception depending on the severity of the crime.

That said, there is some recourse. As Mueller notes in his report -- perhaps suggestively -- the policy "recognizes that a criminal investigation during the President's term is permissible" and that "a President does not have immunity after he leaves office." And, of course, Congress can hasten the end of the President's term through impeachment. So, if a President committed a flagrant and serious crime, such as murder in plain view, I'd expect rapid impeachment followed by indictment, immediately upon removal.

Stephen, Alabama: I see nothing about Trump's finances in the Mueller report. Everyone said, "follow the money." Why was this left out?

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Mueller was appointed special counsel with a specific and limited mandate: investigate "any links or coordination between the Russian government and any individuals associated with the campaign of President Donald Trump; and any matters that arose or may arise directly from the investigation."

But criminal investigations rarely are linear. Prosecutors often discover new and unexpected leads as a case progresses. Indeed, Mueller states in the report that he has referred 14 cases to other prosecutors' offices. Two of those cases are publicly known : (1) the indictment of former Obama White House counsel and Paul Manafort associate Greg Craig for false statements, which landed in the United States Attorney's Office for the District of Columbia, and (2) the Michael Cohen prosecution by the Southern District of New York.

According to CNN, the Southern District also is investigating the Trump Organization and the Trump inaugural committee (though it is unclear if Mueller counts those as part of or separate from the Cohen case), which likely entail a deep dive into Trump's finances and business dealings. (On the matter of the Trump Organization, a spokesperson did not respond to a request for a comment. On the matter of the inaugural committee, a spokesperson for the committee said it intended to comply with Southern District requests.) Regardless, the Southern District's ongoing investigations pose a serious and ongoing threat to Trump, his inner circle and his businesses.

Three questions to watch for next week:

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1) Will Barr make good on his offer to testify in Congress on May 1 and May 2 , and how will he explain his misleading public statements about Mueller's investigation?

2) Will Michael Cohen make last minute efforts to delay or avoid surrendering to federal prison on May 6?