Donald Trump Jr. is not expected to take an oath to tell "the truth, the whole truth and nothing but the truth" when he testifies at the Senate Judiciary Committee Thursday about his meeting with Russians in 2016.

Trump Jr. will talk to the committee in a closed hearing Thursday, but a Democratic member of the committee, Sen. Richard Blumenthal, D-Conn., said he does not think Trump Jr. will be under oath.

"He will probably not be put directly under oath in this setting," Blumenthal said on MSNBC.

But Blumenthal said federal law could still be used to get Trump Jr. in trouble if he lies, even if he is not "under oath."

"The federal statutes make punishable any untruth in these circumstances," he said.

Blumenthal also said he will keep pressuring Republicans to call for Trump Jr. to testify in an open setting, and under oath.

"He will presumably be testifying under oath in public. I have in effect demanded it, others on the committee expect it," he said. "And I think that the chairman [Sen. Chuck Chuck, R-Iowa], who has conducted these hearings in a very impartial, professional straightforward way, will require Donald Trump Jr. to testify in public, under oath."

Trump Jr. will be questioned about the details of his meeting with a Russian lawyer to promised him information about Hillary Clinton. Trump Jr. went to that meeting, along with top campaign aides Jared Kushner and Paul Manafort, but they said the lawyer had no information about Clinton and instead talked about Russia's adoption policy.