The presidential candidate and outspoken Trump critic sounded off on the recent controversy: "He grew up as a very rich kid. I think he's a spoiled brat and I think he thinks he can do whatever he wants to do."

Amid news that House Speaker Nancy Pelosi launched a formal impeachment inquiry of President Donald Trump, Bernie Sanders sounded off on the news during an appearance on The Late Show with Stephen Colbert on Thursday night.

"Donald Trump is probably the most corrupt president in the modern history of this country," the presidential hopeful told the late-night host when asked about the recent controversy. "The impeachment inquiry has got to move as quickly as possible. He is really an embarrassment to our country."

Sanders continued to reiterate that Congress needs to "get moving" on the impeachment inquiry, as he says he's been calling for one "for months." The Vermont senator continued to refer to the controversy as an "outrage on top of an outrage" and proclaimed "enough is enough with this guy."

"This is not complicated and it's consistent with his behavior. I'm not sure that he knows the difference between lying and truth-telling. I doubt he understands what the Constitution of the United States of America is about."

"He grew up as a very rich kid. I think he's a spoiled brat and I think he thinks he can do whatever he wants to do," Sanders said.

"Other people work hard, they tell the truth and pay their taxes. That is not Donald Trump. We have to explain to him what he Constitution of the United States is about."

The impeachment inquiry arrived amid news of a July 25 phone call the president had with Ukrainian President Volodymyr Zelensky in which Trump is said to have asked for help investigating Joe Biden and his son Hunter. In the days before the call, Trump allegedly ordered advisers to freeze $400 million in military aid for Ukraine, prompting speculation that he was holding up the money as leverage for information on the Bidens.

Pelosi called Trump's alleged act a "betrayal of his oath of office." Declaring that "no one is above the law," Pelosi said when announcing the inquiry, "The actions of the Trump presidency revealed dishonorable facts of the president's betrayal of his oath of office, betrayal of his national security and betrayal of the integrity of our elections."

Trump has denied that charge but acknowledged he blocked the funds.

"They're going to lose the election, and they figure this is a thing to do," Trump told reporters. Speaking of Pelosi, he added, "If she does that, they all say that's a positive for me, for the election. You could also say, 'Who needs it? It's bad for the country.'"