Donald Trump is impulsive, loves to talk about himself, and is not interested in details. He is very self confident, and according to his son, has extensive financial relations with Russians.
Perhaps all of this is why it is not surprising that the President decided to volunteer to the Russians visiting his office, "I just fired the head of the FBI. He was crazy, a real nut job. I faced great pressure because of Russia. That's taken off." Mysteriously, Trump excluded the American press from covering this extraordinary meeting in the Oval Office, so the evidence of this admission of obstruction of justice was provided by the Russian press.
This is the smoking gun on the potential charge against the President for "Obstruction of Justice." Like the meeting with the Russians, Trump's potential crimes against our Constitution, which he took an oath to defend, are of his own doing.
1. President Trump said under oath during his inauguration that he will "...faithfully execute the office of President of the United States and, to the best of my ability, preserve, protect and defend the Constitution of the United States." From the Nixon Impeachment in the public records of the Congress, this precedent interpreting this clause of the Constitution, ..."and my constitutional duty to take care that the laws be faithfully executed, [Nixon] has prevented, obstructed and impeded the administration of justice." [which is an impeachable offense].
2. In an interview with NBC Television, Trump said, "I was going to fire Comey, regardless of recommendations....This Russia thing is a made up excuse. He is the wrong man for that position." [in charge of the Russia investigation.]
3. In a Oval Office meeting with Russian officials, Trump said, "I just fired the head of the FBI. He was crazy, a real nut job. I faced great pressure because of Russia. That's taken off."
4. In response to a question by Senator Feinstein on why Comey felt he was fired by Trump said, "I take the president at his word that I was fired because of the Russian investigation--something about the way I was conducting it, the president felt created pressure."
So, in summary, Trump took an oath to not obstruct justice, fired the person leading the investigation of a possible violation of justice (possible crimes against our country), and bragged to our main enemy that he did it [obstructed justice] to relieve great pressure on the Russian investigation.
That sure looks like provable Obstruction of Justice to me--brought on by Trump himself.