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It's the obstruction of justice, stupid!

Updated 9:52 AM ET, Wed December 6, 2017

Washington (CNN) - How much legal peril is President Donald Trump actually in? That's the $1 million question as special counsel Robert Mueller continues to probe Russia's involvement in the 2016 campaign and potential collusion between the foreign power and Trump's presidential team. Trump lawyer John Dowd threw a grenade into that thicket of legal issues earlier this week when he asserted that the President simply cannot obstruct justice.

So, where is all of this going? And how does the legal track being pursued by Mueller jibe -- or not -- with the political end of the investigation? The New Yorker's Jeffrey Toobin gets into all of that (and more!) in his new piece entitled: "Michael Flynn's Guilty Plea Sends Donald Trump's Lawyers Scrambling."

I reached out to Jeff, who is also a CNN contributor, to talk more about his piece and make a few predictions about where the Mueller investigation is headed. Our conversation, conducted via email and lightly edited for flow, is below.

Cillizza: You make an important distinction between the legal case against Trump and the political one. Explain.

Toobin: The legal case, if there is one, would be a criminal indictment of the President -- for obstruction of justice or some other crime. There is a very open constitutional question about whether a sitting President can be indicted, that is, whether the courts will allow such a case to proceed while he is in office.

The argument against such cases is that the President embodies the Executive Branch and the costs imposed by such a case are outweighed by his need to do his duties.

The political case is two-fold, I think. First, there is the possibility of impeachment, for obstruction of justice or some other "high crime and misdemeanors," in the words of the Constitution. The other part of the political case is the day-to-day cost to the President of these various investigations -- in time, attention, focus, and distraction.

Cillizza: The two potential charges against Trump are collusion and obstruction of justice. Which is easier to prove -- based on what we know now -- and why?

Toobin: Obstruction of justice, by a wide margin. It is far from clear that collusion in any form is an actual crime. As I write in my New Yorker article, I see ways that collusion could be prosecuted as a conspiracy to accept illegal campaign contributions from foreigners or as aiding and abetting hacking of email accounts. But there are major factual and legal challenges to any such prosecution that Mueller might bring. By contrast, obstruction of justice is a well-established crime, and there is ample evidence to justify an investigation of the President for a violation. The most compelling evidence, so far, is the firing of FBI Director James Comey.

Cillizza: There's a legal debate raging -- thanks to John Dowd -- over whether a President can even commit a crime like obstruction of justice. Where do you come down on that?

Toobin: I think Dowd confused several issues. As I noted, it is an open question, never addressed by the Supreme Court, whether a President can be indicted while he is in office. This is true for the crime of obstruction of justice or any other crime. By contrast, it is very clear that a President can be impeached for obstruction of justice. Charges of obstruction were central to the impeachment cases against Presidents Nixon and Clinton. So it's clear that the President can commit acts of obstruction of justice -- he is not above the law -- but it's unclear whether that can be addressed in a criminal court as well as in an impeachment proceeding.

Cillizza: In your reporting, did you develop any sense of when Mueller may wrap this up? You note that Trump lawyers keep saying it will happen soon but other evidence contradicts that claim.

Toobin: I don't have a clear sense of when Mueller will wrap up. I very much doubt that he will go on for years, like Kenneth Starr and Lawrence Walsh did. But the Manafort and Gates case is not even scheduled to begin until May 2018, and Flynn just pleaded guilty last week. I think the odds are that Mueller will continue the heart of his work through most of, if not all of, 2018.

Cillizza: Finish this sentence: "The most likely outcome of the Mueller investigation when it comes to Trump is __________." Now, explain.

Toobin: "a report to Congress which will require the House of Representatives to decide whether to begin an impeachment proceeding."

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