Warren wrote in a Tuesday letter to Trump that he appears to be "failing" on his campaign pledge to " 'drain the swamp' of Washington D.C. special interests rigged against the middle class."

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She detailed more than 20 Wall Street or industry "insiders" and "special interest lobbyists" in the letter who are either reportedly being considered for a Trump administration post or are tied to his transition team

"Maintaining a transition team of Washington insiders sends a clear signal to all who are watching you — that you are already breaking your campaign promises to 'drain the swamp' and that you are selling out the American public," she wrote.

Warren added Trump should remove lobbyists from his team, and offered to provide him a list of names of potential replacements. She warned that if Trump refused to change course, she would oppose him "every step of the way for the next four years."

"A lot of what Mr. Trump was saying to get votes, turns out not to be what he intends to do," he said. "[I'm] deeply concerned that a lot of what the president-elect has said on Wall Street, on lobbyists ... on a lot of other subjects are not going to be implemented."

Whitehouse added that Trump should implement his five-point plan for ethics reform, which he outlined during the presidential campaign.

Trump's plan includes banning former government officials from lobbying the federal government for five years after they leave office and a lifetime ban on "senior executive officials" lobbying the government.

Trump acknowledged during a CBS News interview that he has lobbyists on his team, but argued Washington is all "one big lobbyist" and that his administration would "phase that out."

"We’re going to clean it up. We’re having restrictions on foreign money coming in, we’re going to put on term limits, which a lot of people aren’t happy about, but we’re putting on term limits," he said.

"We’re doing a lot of things to clean up the system. But everybody that works for government, they then leave government and they become a lobbyist, essentially. I mean, the whole place is one big lobbyist."