John Dean, the former White House counsel for President Nixon, says there "is enough evidence" for President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE to be impeached.

Dean, who testified against Nixon during the Watergate scandal, told the San Francisco Chronicle in an interview published Monday that Trump's request for Ukrainian President Volodymyr Zelensky to "look into" former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE reaches the threshold to qualify for impeachment.

“There is enough evidence of an abuse of power, a breach of his oath of office,” Dean said. “What they need to do is get evidence that fleshes it out. They need to show exactly what was going on.”

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To speed up the impeachment process, the former White House counsel added that congressional investigators need someone comparable to Dean during the Watergate investigation with extensive White House knowledge to testify against the president.

After initially covering up for Nixon's crimes, Dean cooperated with prosecutors and detailed the violations the president and his staff committed during blockbuster Senate testimony. About a year later, Nixon resigned.

Dean told the newspaper he hoped Don McGahn — the former White House counsel and chief counsel for Trump's campaign — would step up after resigning last October.

“Maybe McGahn will come forward,” Dean said. “He’s got to understand it is not a pleasant route. No one likes to be a tattletale. No one really wants to be a whistleblower unless they’re deeply offended.”

The president's call with Zelensky made up the content of a whistleblower report released to Congress last week. Trump asked the Ukrainian president to investigate Biden and Biden's son's connections in the Ukraine, as Biden's son served on the board of a Ukrainian gas company.

News of the call, which came shortly after Trump delayed hundreds of millions of dollars in aid to Ukraine that had been approved by Congress, sparked Speaker Nancy Pelosi Nancy PelosiDemocratic senator to party: 'A little message discipline wouldn't kill us' Overnight Health Care: New wave of COVID-19 cases builds in US | Florida to lift all coronavirus restrictions on restaurants, bars | Trump stirs questions with 0 drug coupon plan Overnight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds MORE (D-Calif.) to launch an official impeachment inquiry last week.