Is there anything new in this article? Did not seem so. Why is it that so many law professors can look at the same set of known facts and come to such drastically different opinions? (such as alan dershowitz)

Dershowitz isn't discussing the details of obstruction of justice - it is his opinion that the structure of the United States government, as created by the Constitution, imbues the President with executive powers that are incredibly broad. That the Office of President has the power to stop any investigation - even of the President himself - because our Founders wanted the President to have whatever power necessary to protect the Republic as he sees fit.

Therefore, Dershowitz believes it is not theoretically possible for the President to commit Obstruction of Justice because he our Constitution gives him absolute, unfettered, power over the Justice Dept so he can act in the best interests of the United States. For example, imagine Roosevelt was being investigated by the FBI for illegally using the Presidency to illegally transfer several billion dollars into a personal bank account - and that the investigation was ongoing when Japan attacked Pearl Harbor. Dershowitz believes our Constitution is designed to allow Roosevelt to publicly announce something like the following: "I am today ordering the FBI and Justice Departments to close their respective corruption investigations of me. I do this in the interests of national security. The country must focus its attention to the Japanese attack upon Pearl Harbor and I will be asking Congress for a Declaration of War later this afternoon. But I wanted to address the American people first so they understand the need for the actions I am taking this morning. I am not denying the legitimacy of the corruption probes - and I acknowledge I may someday face criminal charges when I am no longer President. But as President, my sole focus, and the sole focus of the Country overall, must be to respond to the fiendish attack by Japan."

Dershowitz argues that the President is always subject to impeachment - but he cannot be charged with Obstruction of Justice because it is an inherent power of the Presidency to stop any investigation for any reason the President wants (or no reason at all). He can be impeached for stopping an investigation, but he cannot ever be charged with Obstruction of Justice because it isn't possible for a President of the United States to obstruct a FBI investigation or hinder a Justice Dpt prosecution.

At the end of the day, however, Dershowitz is playing games and he knows it (for reasons I don't understand). The fact is, it doesn't matter if Trump committed obstruction of justice because the recourse isn't criminal - it is political (i.e. impeachment, which does not require a criminal offense but merely requires a majority vote of the House to Impeach - for whatever reason the House decides).

Sorry for the long winded answer. I hope it helps understand Dershowitz "looking at the forest" approach versus other legal analysts "looking at the trees" (i.e. the details of whether or not the criminal act of impeachment has or has not been satisfied - but again, these so called "experts" are missing the point too because, as noted above, criminality is NOT a requirement for impeachment).