Former US Secretary of State Colin Powell said Sunday that President Donald Trump has "drifted away" from the Constitution and endorsed Democratic candidate Joe Biden for president.

"We have a Constitution. And we have to follow that Constitution. And the President has drifted away from it," Powell, who served under President George W. Bush, told CNN's Jake Tapper on "State of the Union."

Powell said he's "proud" of what a number of former generals, admirals and diplomats have said about Trump's response last week to the widespread protests following the death of George Floyd, adding that he hadn't released a public statement denouncing Trump's response because he felt he had demonstrated his displeasure with Trump in 2016 when he voted against him.

"I think what we're seeing now, is (the most) massive protest movement I have ever seen in my life, I think it suggests the country is getting wise to this and we're not going to put up with it anymore," the retired general told Tapper.

In contrast, he called out Republican lawmakers for largely staying silent on Trump's response last week to the national unrest.

"I watched the senators heading into the chamber the other day after all this broke, with the reporters saying, 'What do you have to say? What do they you to say?'" he said.

Powell also said he is he is planning to vote for Democrat Joe Biden for President in November, again voting against Trump as he had done in 2016.

"I'm very close to Joe Biden on a social matter and on a political matter. I worked with him for 35, 40 years, and he is now the candidate and I will be voting for him," he said.

Asked why it was so important to him that Trump not be reelected, Powell said that he thinks Trump has not been an effective president and that he lies "all the time."

"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 to get out of the situation that we find ourselves in now," he told Tapper. "We're America, we're Americans, we can do this. We have the ability to do it, and we ought to do it. Make America not just great, but strong and great for all Americans, not just a couple."

Trump attacked Powell on Twitter shortly after his interview Sunday, referring to him as "a real stiff" and Biden as "another stiff." Trump also lashed out at the former Secretary of State for his role in presenting the US' case against Iraq to the United Nations in 2003.

The comments follow the criticism of former Defense Secretary James Mattis, who last week issued a fiery statement in which he condemned Trump for his handling of the protests over George Floyd’s death.

Mattis accused Trump of being the first President in his lifetime “who does not try to unite the American people—does not even pretend to try.”

Mattis’ sharp criticism followed Trump’s threat earlier this week to deploy US troops to states to quell protests. It also followed the incident in which law enforcement fired tear gas and rubber bullets at protesters outside the White House before Trump walked to the nearby St. John's Episcopal Church to take a photo.

Asked by Tapper if he agreed specifically with Mattis' comments, Powell doubled down on his criticism of Trump.

"You have to agree with it. I mean, look at what he has done to divide us," he said. "I agree with all of my former colleagues."

"I'm proud of what they're doing. I'm proud that they were willing to take the risk of speaking honesty and speaking truth to those who are not speaking truth," Powell added.