Despite providing political ammunition to Trump’s foes, former FBI director James Comey’s statement on his dealings with the president actually weakens the case for obstruction of justice, argues Harvard law professor Alan Dershowitz:

“Former FBI Director James Comey’s written statement, which was released in advance of his Thursday testimony before the Senate Intelligence Committee, does not provide evidence that President Trump committed obstruction of justice or any other crime. Indeed it strongly suggests that even under the broadest reasonable definition of obstruction, no such crime was committed.

[…]

Comey understood ‘the President to be requesting that we drop any investigation of Flynn in connection with false statements about his conversations with the Russian ambassador in December.’

[…] He was troubled by what he regarded as a breach of recent traditions of FBI independence from the White House, though he recognized that ‘throughout history, some presidents have decided that because “problems” come from the Department of Justice, they should try to hold the Department close.’

That is an understatement.

Throughout American history — from Adams to Jefferson to Lincoln to Roosevelt to Kennedy to Obama — presidents have directed (not merely requested) the Justice Department to investigate, prosecute (or not prosecute) specific individuals or categories of individuals.

[…]

In Great Britain, Israel and other democracies that respect the rule of law, the Director of Public Prosecution or the Attorney General are law enforcement officials who, by law, are independent of the Prime Minister.

But our constitution makes the Attorney General both the chief prosecutor and the chief political adviser to the president on matters of justice and law enforcement.

[…]

Assume, for argument’s sake, that the President had said the following to Comey: ‘You are no longer authorized to investigate Flynn because I have decided to pardon him.’ Would that exercise of the president’s constitutional power to pardon constitute a criminal obstruction of justice? Of course not. Presidents do that all the time.

The first President Bush pardoned Caspar Weinberger, his Secretary of Defense, in the middle of an investigation that could have incriminated Bush. That was not an obstruction and neither would a pardon of Flynn have been a crime. A president cannot be charged with a crime for properly exercising his constitutional authority

For the same reason, President Trump cannot be charged with obstruction for firing Comey, as he had the constitutional authority to do.”