WASHINGTON -- Sen. Dianne Feinstein, D-California, issued a stern warning to President Donald Trump in the wake of a turbulent few weeks for the White House.

"Stop tweeting, think about what you say because you're reflecting in a big pool," Feinstein said Sunday on "Face the Nation."

"The Senate and the House have to feel a sense of stability from day to day. We can't feel the anxiety that goes with not knowing what may happen next, what may be said next. And we need to depend on our president for truth. That is really important," Feinstein added.

It's also important for the American people to know what could be behind "some of the actions that have recently been taken," Feinstein said. And she has questions for former FBI Director James Comey, who was recently fired.

"What I want to know from him is how many times did he meet with the president. Or talk with the president on the phone. What was he asked by the president? Was he asked to in any way alter the investigation? What was he asked about General Flynn? Questions like that," said Feinstein.

Feinstein's comments come after a series of dramatic events, including the appointment of former FBI Director Robert Mueller to oversee the Trump-Russia probe, and revelations of a Comey memo that said Mr. Trump pressed him to drop the investigation into former National Security Adviser Michael Flynn.

When asked if the investigation now goes beyond the question of Russia and the Trump campaign and includes a question of a cover-up, Feinstein said, "Well, I think that's right. It does. I know what the president told me when he called to say that he was firing him. And that turned out not to be the reason."

Feinstein, the top Democrat on the Senate Judiciary Committee, had repeatedly called for public hearings to find out the details surrounding Mr. Trump's reported request to end the Flynn investigation.

Following the appointment of Mueller as a special counsel in charge of the Russia investigation, Feinstein applauded Deputy Attorney General Rod Rosenstein's pick, calling the former FBI director "respected" and "talented."

"The appointment of Bob Mueller as special counsel for the Russian investigation is a good first step to get to the bottom of the many questions we have about Russian interference in our election and possible ties to the president," Feinstein said in a previous statement. "Bob was a fine U.S. attorney, a great FBI director and there's no better person who could be asked to perform this function.

Comey has recently agreed to testify in public before Senate Intelligence Committee members to discuss the events surrounding his firing, a move Feinstein says is important in order to "put the facts before the American people."

"The big fact is: Did the president fire Comey because of his investigation and he was worried about what the investigation might conclude? If so, that borders on a very serious charge. So we need to flesh that out. We need to see what the response is. And it's got to come from Director Comey himself," said Feinstein.

Feinstein was asked about comments that -- according to The New York Times -- Mr. Trump made in a meeting with Russians. Mr. Trump reportedly called Comey a "nut job" and said his firing relieved "great pressure" on him -- comments that Feinstein called a "horrible thing for a president to say."

"Former Director Comey is no way, shape, or form a nut job," she said. "He's a very strong man. He's very principled man. I happen to believe he made a couple of mistakes. I suspect he thinks he's made a couple of mistakes. Whether that deserved his termination or not is not up to me. The fact is he has been terminated. But the reason for the termination has really not been ferreted out. And that's what has to be before the American people clear and distinct."