(Bloomberg) -- Former Secretary of State Colin Powell criticized President Donald Trump for threatening to use active-duty U.S. troops against protesters, saying it shows he has “drifted away” from the U.S. Constitution.

In a CNN interview, Powell aimed a broad critique at Trump’s approach to the military, a foreign policy he said was causing “disdain” abroad and a president he portrayed as trying to amass excessive power. Powell, who served under Republican President George W. Bush, said he’ll vote for Democrat Joe Biden in the general election.

“We have a constitution and we have to follow the constitution and the president has drifted away from it,” Powell said on CNN’s “State of the Union” on Sunday.

Trump responded swiftly on Twitter, mocking Powell’s intention to vote for his likely Democratic opponent and calling the retired four-star general “a real stiff” who got the U.S. into wars after the September 11, 2001 terrorist attacks on the U.S.

The president followed up by calling Powell, 83, a four-star general, former chairman of the Joint Chiefs of Staff, and former National Security Adviser, “highly overrated” in running through his policy achievements.

Trump’s threat to use troops against protesters has drawn high-profile criticism from several former military leaders, including former Defense Secretary Jim Mattis and former Chief of Staff John Kelly.

More than a week of demonstrations against police brutality across the U.S. initially turned violent in some cities, though they’ve recently been mostly peaceful. On Sunday, Trump ordered the National Guard to start withdrawing from Washington D.C. after a massive but peaceful protest in the city Saturday.

Powell said Trump needs to understand the Constitution and the restraints on him. He urged members of the Congress to step up, and said he’s “proud” of his former military colleagues who spoke out against Trump.

Powell said he’s “very close” to Biden on social and political issues and would speak out for him during the election campaign.

He portrayed the protests as signs of a broader public dissatisfaction with Trump, racism and wealth and education gaps.

“The economy exists for all of the American people, not just you doing great or me doing better,” Powell said. “So what we have to do now is reach out to the whole people, watch these demonstrations, watch these protests -- and rather than curse them, embrace them to see what it is we have to do get out of this situation that we find ourselves in now.”

(Updates with additional comments from fifth paragraph.)

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