Colin Powell, former US secretary of state and a board member of Bloom Energy Corp., pauses during a group interview with Masayoshi Son, chairman and chief executive officer of SoftBank Corp., in Tokyo, Japan, on June 17, 2014.  (KIYOSHI OTA / BLOOMBERG)

Colin Powell on Sunday became the latest notable Republican or former military leader to express concern about President Donald Trump, saying he’ll vote for Joe Biden in November instead.

The former secretary of State said that by threatening last week to use active-duty US troops against protesters, Trump showed he has “drifted away” from the US Constitution.

“He is now the candidate, and I’ll be voting for him,” Powell, perhaps the most prominent black Republican in the US, said of Biden on CNN’s “State of the Union.”

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Powell, 83, was the top diplomat under Republican President George W. Bush and before that served as chairman of the Joint Chiefs of Staff and as National Security Adviser.

We have a Constitution and we have to follow the Constitution, and the president has drifted away from it.

Colin Powell, Former US secretary of state

He joins a number of prominent retired military officials as well as current and former lawmakers to criticize Trump, although not all have said they’ll vote for Biden. Powell has also said he didn’t vote for Trump in 2016.

Senator Mitt Romney of Utah, a long-term antagonist of Trump, has suggested he’ll write in his wife’s name in November. The New York Times reported that Cindy McCain, widow of Republican Senator John McCain, is likely to vote for Biden. Senator Lisa Murkowski of Alaska said last week’s she’s “struggling” to support Trump. And former President George W. Bush and his brother Jeb, a former Florida governor, are other possible Biden voters.

Broad critique

Powell on Sunday 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.

“We have a Constitution and we have to follow the Constitution, and the president has drifted away from it,” Powell said. Trump also, he said, “lies about things.”

Trump responded swiftly on Twitter, mocking Powell and calling the retired four-star general “a real stiff” who got the US into wars after the Sept 11, 2001, terrorist attacks on the US.

The president followed up by calling Powell, “highly overrated,” and running through his own policy actions.

Similarly, on Friday, Trump said he would back any candidate, “good or bad,” against Murkowski in 2022, when she’s up for re-election. “If you have a pulse, I’m with you,” the president tweeted.

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

Mattis said in a statement on Wednesday that Trump had abused his power when a park across the street from the White House was forcibly cleared of peaceful protesters before the president staged a photo op at a nearby church damaged by arson.

READ MORE: After long silence, Mattis denounces Trump, military response

“We must reject and hold accountable those in office who would make a mockery of our Constitution,” the former defense secretary and former Marine Corps commander said.

Murkowsi told reporters that Mattis’s critique of Trump was “necessary and overdue.”

More than a week of demonstrations have been held against police brutality across the US While initially they turned violent in some cities, they’ve recently been mostly peaceful. On Sunday, Trump ordered the National Guard to start withdrawing from Washington.

Constitutional restraints

Powell said Trump needs to understand the restraints on him contained in the US Constitution. 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 also said he’s “very close” to Biden on social and political issues and would speak out for him during the election campaign.

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A number of other former military officials - whose political leanings, if any, are often unknown -- continued to criticize Trump on Sunday political talk shows.

“Many of us watched the use of active-duty military to clear peaceful protesters out of Lafayette Square, and it rang echoes of what the founders feared more than anything, which was the use of armed active-duty military against citizens,” retired Admiral James Stavridis said on NBC’s “Meet the Press.”

A “whole spectrum” of former military leaders “jumped and felt that shock of watching active-duty troops clear peaceful protesters. Wrong answer,” said Stavridis, former supreme allied commander of NATO. Stavridis is also a Bloomberg Opinion columnist.

“Our military should never be called to fight our own people as enemies of the state. And that quite frankly for me really tipped it over,” retired Admiral Mike Mullen, former chairman of the Joint Chiefs of Staff, said on “Fox News Sunday.”

Mullen wrote a widely cited essay for The Atlantic magazine last week criticizing the decision to use members of the National Guard and other security personnel to clear Lafayette Square near the White House last week.

Others who’ve spoken up recently include retired Navy Admiral William McRaven, director of the raid that killed Osama bin Laden. There was “nothing morally right” about the decision to clear peaceful protesters, he said.

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