In that article, Senator Bob Corker states the obvious, but does not go nearly far enough.
“Like me, most Americans hope that our justice system is independent and free of political interference,” Corker said in a statement. “President Trump’s pressuring of the Justice Department and FBI to pursue cases against his adversaries and calling for punishment before trials take place are totally inappropriate and not only undermine our justice system but erode the American people’s confidence in our institutions.”
What Trump said:
"The saddest thing is that because I'm the President of the United States, I am not supposed to be involved with the Justice Department," Trump said. "I am not supposed to be involved with the FBI."
"At some point the Justice Department, and the FBI, must do what is right and proper. The American public deserves it!"
Please notice, he does NOT say “I CANNOT.” He says “I am not supposed to.”
I went to Nixon’s articles of impeachment, and while perusing saw in Article II Abuse of Power, summary:
[President Nixon] repeatedly engaged in conduct violating the constitutional rights of citizens, impairing the due and proper administration of justice and the conduct of lawful inquiries, or contravening the laws governing agencies of the executive branch and the purposed of these agencies.
More particularly, by firing James Comey, and admitting it was because of “this Russia thing”:
….interfering or endeavoring to interfere with the conduct of investigations by the Department of Justice of the United States, the Federal Bureau of Investigation, the office of Watergate Special Prosecution Force, and Congressional Committees
And in this following instance going even beyond Nixon, by declaring, AS PRESIDENT OF THE UNITED STATES, that this investigation is a “witch hunt.” (Nixon merely claimed that HIS investigation was thorough and complete.) Trump never even had it looked into.
….making or causing to be made false or misleading public statements for the purpose of deceiving the people of the United States into believing that a thorough and complete investigation had been conducted with respect to allegations of misconduct on the part of personnel of the executive branch of the United States and personnel of the Committee for the Re-election of the President, and that there was no involvement of such personnel in such misconduct
One could also argue that with the pardoning of Joe Arpaio, BEFORE SENTENCING HAD EVEN TAKEN PLACE, Trump may be guilty of this also:
endeavoring to cause prospective defendants, and individuals duly tried and convicted, to expect favored treatment and consideration in return for their silence or false testimony, or rewarding individuals for their silence or false testimony.
And finally, on to what Senator Corker alludes to, Trump’s dismay that he cannot do what Nixon was being impeached for:
In disregard of the rule of law, he knowingly misused the executive power by interfering with agencies of the executive branch, including the Federal Bureau of Investigation, the Criminal Division, and the Office of Watergate Special Prosecution Force, of the Department of Justice, and the Central Intelligence Agency, in violation of his duty to take care that the laws be faithfully executed.