It would be a mistake for special counsel Robert Mueller not to subpoena President Donald Trump to appear before a grand jury in the investigation of Russian interference in the 2016 election, said House Intelligence Committee Chairman Adam Schiff.

Mueller is constrained by time pressure to conclude his work and also faces a White House that would likely fight a subpoena, Schiff said. Even so, he shouldn't rely just on written answers from Trump because lawyers help craft them and there's no chance for follow-up questions, the California Democratic lawmaker said Sunday on NBC's "Meet the Press."

"Probably the best way to get the truth would be to put the president under oath," Schiff said. "Because as he's made plain in the past, he feels it's perfectly fine to lie to the public. After all, he has said, 'It's not like I'm talking before a magistrate.' Well, maybe he should talk before a magistrate."

Trump's lawyers have suggested that the president won't be sitting down with Mueller to answer questions beyond written responses to some queries that were submitted in November. The attorneys have said the answers only cover events before Trump became president and Russian-related topics, not whether he tried to obstruct justice.

Trump has repeatedly denied any wrongdoing and collusion between his campaign and Russia, and derided Mueller's investigation as a witch hunt.

There are expectations in Washington that Mueller will wrap up his investigation and send his findings to U.S. Attorney General William Barr within days or weeks.

"I've said all along that I don't think Bob Mueller should rely on written answers," Schiff said.