Here's the most important question Robert Mueller wants to ask Donald Trump

(CNN)President Donald Trump took to Twitter on Tuesday morning to complain about the ongoing special counsel investigation into Russian meddling in the 2016 election. He tweeted this: "It would seem very hard to obstruct justice for a crime that never happened! Witch Hunt!"

Though I am not a lawyer, that sounded off to me. So I reached out to Carrie Cordero, who is a lawyer -- and an adjunct senior fellow at the Center for a New American Security. (Cordero is also a CNN legal analyst.)
Our conversation, conducted via email and lightly edited for flow, is below.
Cillizza: Donald Trump tweeted Tuesday morning that there can't be obstruction of justice because there is no crime. Is he right?
    Cordero: No, on several levels. Setting aside for a moment the issue of whether the President can be charged with a crime, generally, one can be charged and found guilty of obstruction of justice, even if there are no other charges successfully brought against the person charged with obstruction, or, others.
    There are several different statutory obstruction provisions, but, to summarize, obstruction pertains to corruptly influencing or obstructing a proceeding or the administration of justice. The FBI and Justice Department, and, since May 18, 2017, the special counsel, have been conducting an investigation into Russian influence on the 2016 election. And the special counsel is authorized to investigate other matters that may arise during the course of the investigation, under the ongoing supervision of Rod Rosenstein, who is the acting attorney general for purposes of this investigation.
    Obstruction need not be one specific act. An obstruction case could be developed against the President (again, with the caveat, above) based on a pattern of activity. Based on his public statements, including tweets, and what has been revealed publicly through other sources about things he said and did privately, the special counsel could be exploring whether he, with corrupt intent, endeavored to obstruct the ongoing investigation. The investigation includes proceedings before a federal grand jury. Among other things, one could argue the President has done a variety of things that could establish a pattern of obstruction, such as his activities to intimidate or pressure investigators and witnesses; exert improper influence to end the investigation; fire the chief investigator, then-FBI Director James Comey; encourage and succeed in firing his successor, Deputy Director Andrew McCabe; and consider firing the attorney general and deputy attorney general so as to influence the overall supervision and direction of the investigation.
    In addition, there are specific lanes of the special counsel's investigation that have already led to criminal charges, and, in some cases, guilty pleas. Let's take the easiest example, the case of former assistant to the President for national security, Michael Flynn. According to a credible witness (named James Comey), Trump asked then-Director Comey to let the Flynn case "go." At the time, the FBI was conducting an investigation of Flynn for, at least, violations of the Foreign Agents Registration Act. He later pleaded guilty to making false statements to the FBI during the course of its investigation.
    In this case, if the special counsel's office assesses that the specific statement made by Trump, plus other actions or statements he made specific to the Flynn case make a credible case of obstruction, then, at least as it pertains to this one aspect, his efforts to disrupt an investigation involve an investigation that has already resulted in criminal charges and a guilty plea. Stated plainly, there are already crimes that have been established.
    Cillizza: Trump -- in tweets and public statements -- seems very focused on the idea that neither he nor anyone in his campaign colluded with the Russians. Let's say he (and they) didn't. Is he out of the woods as it relates to Mueller?
    Cordero: No, again. We've heard a lot in the public discussion about how "collusion isn't a crime." This is true in the literal sense: there is no section in the criminal code that says "it is a crime for a political campaign to 'collude' with a foreign power in order to win an election." But it is a violation of campaign finance laws to receive foreign money in a political campaign. It is a crime to assist with or be an accessory to computer hacking. Whether individuals on the Trump campaign did these things, we don't know yet. But if they did, there are criminal violations that could apply.
    In addition, the special counsel's overarching theory of the case appears to be that the activities undertaken by Russia to influence the 2016 election broadly fall into the category of "conspiracy to defraud the United States," which is a federal crime. We see this conspiracy charge in the indictment of the Internet Research Agency, the Russian government front organization that directed social media activities against the United States. Conspiracy is also a charge that can (and has already in this investigation) accompany allegations of financial crimes.
    So, there is still a risk -- not just to the President but to individuals involved in his campaign -- that they could face a conspiracy charge for activities that took place in furtherance of the Russian-government sponsored conspiracy.
    Cillizza: Let's take a step back: What do the leaked questions Mueller wants to ask Trump tell you about the investigation?
    Cordero: The questions, which I take to be a summary of the major themes and topics that the special counsel's office wishes to interview the President about, track with the topics that have been revealed through open congressional hearings, news reporting, and the existing criminal charges that have issued from the special counsel's investigation.
    One of the major takeaways from the questions is that his statements and tweets do matter, in a legal sense. This would be true of anyone else facing investigation, so it makes sense that it would apply to the President as well. One's statements matter. So, when he tweets something that indicates his mindset, or his intent, those statements are relevant to the investigation and can be used as evidence. Why did he routinely praise WikiLeaks during the summer of 2016? Why did he tell Sergey Lavrov the pressure was off after he fired Comey? Why did he tell NBC's Lester Holt he fired Comey because of the Russia investigation? The answers to these questions matter.
    But the public disclosure of the questions themselves tells us something, too. The disclosure of these questions to a reporter sheds light on the dysfunction of the White House and the President's legal team. If a lawyer working on the President's team leaked them, that person is arguably violating an ethical duty of confidentiality to the client. If someone other than a lawyer in the White House leaked them, then why such loose control of important documents? If these questions resulted from meetings between the special counsel's team and the President's legal team, someone who is involved in very sensitive conversations -- the potential interview by a prosecutor of the President of the United States for a wide-ranging investigation in which campaign officials have already been charged and, in some cases pleaded guilty -- thought the document belonged in the public domain. Why?
    Cillizza: Was there a question (or more) that surprised you in there? Why or why not?
    Cordero: I wasn't surprised by any particular question, but the the question that was most interesting to me was also the question that (Times reporter) Michael Schmidt flagged as "intriguing":
    • "What knowledge did you have of any outreach by your campaign, including by Paul Manafort, to Russia about potential assistance to the campaign?"
    Here's why: "Assistance" could cover a variety of activities, including the propaganda activities conducted by the Russian-sponsored entities and individuals, the social media campaign, and the overall disruption efforts.
    But, in my view, the big wild card in this investigation concerns money. Paul Manafort and Richard Gates were money guys. They were adept at moving money around the world, dealing with shady Russian oligarchs and the like. As revealed through their indictments, they knew how to launder money through a variety of schemes, all of which evaded government scrutiny until the special counsel's investigation focused on them. This question seems, at least in part, intended to elicit whether there was outreach on behalf of the campaign to solicit financial support from prohibited persons or entities, and if there was, whether Trump knew about it personally.
    Cillizza: Finish this sentence: "Donald Trump ____________ sit down with Robert Mueller before the end of the special counsel probe." Now, explain.
    Cordero: Brutal question. Who among us knows what Donald Trump is going to do next? As best as I can tell, he has not even made up his own mind about whether to submit to a voluntary interview with the special counsel's team. And given the revolving door on his legal team over the past year, it's quite possible that he is being given conflicting advice about whether he should do so, or not.
    Leaving out the political considerations of what it would look like for a President to refuse an interview altogether, there are significant aspects of the investigation that would be illuminated by the President's direct interview. A candidate is the head of his own campaign: what he knew or did not know about meetings and communications with Russian government officials and surrogates is highly relevant to the investigation. On obstruction, intent is a central element, so what he was thinking when he took certain actions, tweeted certain tweets or said specific things to other government officials, is also highly relevant to that aspect of the investigation. None of this suggests that it is necessarily in Donald Trump's personal interests to submit for a voluntary interview. If he does not submit to a voluntary interview, the special counsel could issue a subpoena for him to testify before a grand jury. He then would either need to answer questions under oath, or, assert his constitutional rights not to answer.