Washington (CNN) GOP Sen. Jeff Flake gave some of his harshest criticism of President Donald Trump to date in a commencement speech Wednesday to Harvard Law students, where he shared his concerns for the integrity of politics in the United States.

The Arizona senator, who has announced he will not be seeking re-election in 2018, has said he will use his remaining time in the Senate to speak out against the President when he believes it is warranted.

"Not to be unpleasant, but I do bring news from our nation's capital. First, the good news: Your national leadership is ... not good," he said at the commencement Wednesday. "At all. Our presidency has been debased. By a figure who has a seemingly bottomless appetite for destruction and division. And only a passing familiarity with how the Constitution works."

He later continued: "Now, you might reasonably ask, where is the good news in that? Well, simply put: We may have hit bottom. Oh, and that's also the bad news. In a rare convergence, the good news and bad news are the same: Our leadership is not good, but it probably can't get much worse."

In an interview with CNN's "The Situation Room with Wolf Blitzer, Flake said his speech was about standing up and reclaiming "our constitutional prerogative."

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