At a press conference with Speaker Nancy Pelosi (D-Calif.) on Wednesday, House Intelligence Chairman Adam Schiff (D-Calif.) condemned President Trump's tweets demanding to "meet" the Ukraine whistleblower as "a blatant effort to intimidate witnesses" and "an incitement of violence."

"We will do everything in our power to make sure that whistleblower is protected. That the whistleblower's preferences in terms of their anonymity are respected. Let's not make any mistakes here. The president wants to make this all about the whistleblower, and suggests people that come forward with evidence of his wrongdoing are somehow treasonous and should be treated as traitors and spies. This is a blatant effort to intimidate a witness. It's an incitement of violence. "

Why it matters: Democrats and some Republicans have spoken out against Trump's tweets calling for the whistleblower's identity to be revealed and suggesting that they are some type of spy.

Sen. Chuck Grassley (R-Iowa) released a statement on Tuesday stressing that the Ukraine whistleblower, who has set off an impeachment inquiry into President Trump, "ought to be heard and protected."

2020 candidate Sen. Kamala Harris (D-Calif.) sent a letter to Twitter CEO Jack Dorsey on Wednesday asking him to suspend Trump's account for violating Twitter's rules by accusing the whistleblower of being a spy and Schiff of treason.

The big picture: Schiff also said during the press conference that attempts by the White House or the State Department to defy subpoenas or block witnesses from testifying will be considered evidence of obstruction in the impeachment inquiry.

Go deeper: Intelligence community watchdog refutes Trump's whistleblower claims