CNN  — 

President Donald Trump disparaged Rep. Adam Schiff in a profane tweet Sunday, misspelling his name “Schitt” and accusing the likely incoming House Intelligence chairman of baselessly criticizing the appointment of acting Attorney General Matt Whitaker.

“So funny to see little Adam Schitt (D-CA) talking about the fact that Acting Attorney General Matt Whitaker was not approved by the Senate, but not mentioning the fact that Bob Mueller (who is highly conflicted) was not approved by the Senate!” Trump wrote.

Special counsel Robert Mueller was appointed by Deputy Attorney General Rod Rosenstein, and like many other Department of Justice appointees, he did not require Senate confirmation for the position.

The White House did not immediately return CNN’s request for comment Sunday evening on whether Trump purposely misspelled Schiff’s name.

Democrats have criticized Trump’s appointment of Whitaker, who now oversees Mueller’s probe into Russian interference in the 2016 election, citing the appointee’s past criticisms of the investigation.

Some Democratic lawmakers, such as Schiff, and some legal scholars – including George Conway, the husband of Trump counselor Kellyanne Conway – have also criticized Whitaker’s appointment as unconstitutional because he was not confirmed by the Senate. Yet others have argued that the appointment is valid because he’s only serving on a temporary basis under the Federal Vacancies Act.

After firing former Attorney General Jeff Sessions, who angered Trump by recusing himself from issues related to the 2016 campaign, the President chose Whitaker over Rosenstein, who had overseen the Mueller probe.

Mueller’s appointment and constitutional authority was upheld in August by a federal judge appointed by Trump, who wrote in an opinion that Mueller’s “appointment does not violate core separation-of-powers principles.”

Schiff shot back at Trump on Sunday, insinuating in a tweet that the President’s lawyers are writing Trump’s answers to Mueller’s questions in the Russia investigation for the President.

Trump told reporters on Friday that he was personally crafting the answers to Mueller, saying, “My lawyers don’t write answers. I write answers. I was asked a series of questions. I’ve answered them very easily.”

In his response to Trump’s name-calling tweet on Sunday, Schiff wrote, “Wow, Mr. President, that’s a good one. Was that like your answers to Mr. Mueller’s questions, or did you write this one yourself?”

In an interview on ABC News’ “This Week” Sunday morning, Schiff said that Whitaker’s appointment was unconstitutional and would not hold up in court.

“I think the appointment is unconstitutional,” Schiff said. “He is clearly a principal officer, and the fact that he is a temporary principal officer doesn’t mean that that is any less subject to Senate confirmation. Constitutionally it has to be subject to confirmation. I think they’d lose that court – that case when it goes to the Supreme Court.”

Schiff promised that House Democrats would investigate Whitaker’s appointment once they take the majority in January.

“He needs to know that if he takes any action to curb what Mr. Mueller does, we’re going to find out about it, we’re going to expose it,” he said.