During President Trump’s impeachment trial this week, lawyers for the president have made the remarkable claim that it is impermissible for the Senate to consider Trump’s state of mind. Alan Dershowitz argued that determining whether the president abused his power in withholding military aid to Ukraine would require the Senate improperly to “psychoanalyze” the president. Patrick Philbin, deputy counsel to the president, also argued it would be impermissible to convict the president based on the “reason in the president’s mind” for his actions. But this is nonsense. Not only is proof of the president’s intent permissible, it’s essential — which makes it all the more critical that former national security adviser John Bolton be called to testify.

Almost all criminal law requires proof of the defendant’s intent. Indeed, it’s usually the key issue in white-collar offenses such as bribery or obstruction of justice, which are embodied in the text of the articles of impeachment. In such cases, proof of what was in the defendant’s mind is usually what distinguishes an otherwise lawful act from a criminal offense.

Suppose prosecutors have a member of Congress on video accepting an envelope full of cash from me. That alone proves relatively little: It could be a legal campaign contribution, or I could be purchasing his Washington Nationals season tickets. To prove it was a bribe, prosecutors would have to show that he accepted the money with the corrupt intent to be influenced in the performance of some official act. In other words, prosecutors would have to prove why he took the money — what was in his mind.

Or suppose I take my laptop and smash it with a hammer. If I do it in a fit of anger because it crashed one too many times, it may be rash, but it’s perfectly lawful. But if I do it because a grand jury has subpoenaed the documents on the laptop and I want to keep that information from the grand jury, I have now committed obstruction of justice — based solely on the reason in my mind for performing the otherwise lawful act.

Dershowitz is not new to this type of argument. He made similar claims during special counsel Robert S. Mueller III’s investigation. Dershowitz argued that a president could not be charged with obstruction of justice for an otherwise legitimate exercise of executive authority, such as firing the FBI director, even if the president acted corruptly. A crime, he claimed, cannot be based on “what was in the president’s mind.” (In the legal analysis portion of his report, Mueller properly rejected this argument.)

But even Dershowitz doesn’t really believe you can never examine a president’s intent. For example, he agrees a president could be impeached and removed for the crime of bribery. But as I noted above, proving bribery requires proof why the president accepted something of value. In other words, it requires proof of what was in the president’s mind — the very thing that Dershowitz says is impermissible.

In short, proof of state of mind is not only commonplace, it’s indispensable. If Trump withheld the aid to Ukraine because he was honestly concerned about corruption in that country, that would be a defense. If he took the exact same action for the corrupt reason of pressuring Ukraine to announce investigations that would benefit him personally and politically, that would constitute bribery and an abuse of power. Everything hinges on the president’s state of mind.

This is where Bolton comes in. Given our inability to read minds, prosecutors often have to prove corrupt intent through circumstantial evidence. They accumulate evidence of the surrounding events and actions by the defendant and others until the conclusion of corrupt intent becomes inescapable. This describes much of the case the House sent over with its articles of impeachment: The president’s actions, the testimony and actions of those around him, and the absence of any other credible explanation for withholding the aid to Ukraine, all provide compelling evidence of Trump’s intent.

But the best way to prove intent is through a defendant’s own statements. The record from the House investigations does include some statements by the president, including the rough transcript of his July 25 phone call with Ukrainian President Volodymyr Zelensky during which he asked for a “favor.” But Bolton is the first witness to come forward and claim to have heard Trump himself explicitly say that the hold on aid was linked to Ukraine’s agreement to announce investigations into the Bidens. This is critical, direct evidence of intent that goes to the very heart of the charges against the president. Senators who are interested in the truth should want to hear it.

Contrary to the arguments of the president’s lawyers, it’s not improper for the Senate to consider what was in the president’s mind. Juries make these determinations every day in deciding whether to find a defendant guilty and send him to prison. The Senate can certainly do so when deciding whether a president should remain in office.

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