Legal question swirls around Trump: What constitutes obstruction of justice?

During his career, James Comey has served as a federal prosecutor, senior Justice Department official, corporate lawyer, and FBI director. With the release of his memoir on Tuesday, he is about to become a bestselling author.

But Mr. Comey’s most significant role may be yet to come.

If special counsel Robert Mueller’s investigation proceeds as many Trump critics are hoping, Comey could eventually emerge as the star witness at a congressional trial to possibly impeach President Trump for alleged obstruction of justice.

That goes a long way to explain why Comey is under such vicious attack on Twitter and elsewhere by the president and his supporters.

“Slippery James Comey… will go down as the WORST FBI director in history, by far,” Mr. Trump tweeted on Sunday.

In his book, “A Higher Loyalty:

Often a key to impeachment trialsAn unresolved legal question