Democratic Rep. Maxine Waters Maxine Moore WatersPowell, Mnuchin stress limits of current emergency lending programs Pelosi: House will stay in session until agreement is reached on coronavirus relief Omar invokes father's death from coronavirus in reaction to Woodward book MORE (Calif.) tore into President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE and Republicans in Congress on Wednesday for questioning the integrity of the special counsel's investigation.

Speaking on "All In with Chris Hayes," Waters stressed that Republicans' increased attacks on special counsel Robert Mueller's team revealed the administration's desperation to stop the probe.

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"We don't know everything that's in this plot, except that they're trying to stop this investigation," Waters told Hayes. "This president does not want it to go forward and we cannot help but ask: Why?"

"What is he afraid of?" she continued. "If he has not been involved with collusion, if he has not been involved in obstruction of justice, if he has not been involved in money laundering, if he doesn't have a plot to lift the sanctions working with the Kremlin, and the oligarchs of Russia, [then] what is he afraid of?"

"Why is he going to such lengths to discredit the special counsel?" she asked.

Waters, a top critic of Trump and his administration, joined Rep. Ted Lieu (D-Calif.) and other Democrats in warning that Trump's attacks on the special counsel office could be a prelude to Mueller's firing.

"If Donald Trump wants to take the first footsteps of Richard Nixon, he's certainly welcome to try," Lieu warned Wednesday in a speech on the House floor. "But it will not end well for him."

The White House has repeatedly denied rumors that Trump is considering firing Mueller.

"As the White House has repeatedly and emphatically said for months, there is no consideration at the White House of terminating the special counsel,” Trump's lawyer Ty Cobb said last week.