US President Donald Trump said in a television interview airing Sunday that he does not know whether he must uphold the US Constitution.

He also said he is not seriously considering running for a third White House term, after musing publicly over an idea clearly barred by the nation's founding legal document.

"I don't know," Trump responded when the host of NBC News "Meet the Press with Kristen Welker" asked directly whether he believes he needs to uphold the supreme law of the land.

Asked specifically whether American citizens and non-citizens alike deserve the due process of law, as the US Constitution states, Trump said, "I'm not a lawyer. I don't know."

The president's aggressive moves to deport undocumented migrants — some without the benefit of a court hearing — have drawn widespread criticism, but Trump insists it is necessary in the face of what he has declared to be a "national emergency."

The suggestion of possibly seeking a third term in office has been sharply questioned by legal and constitutional scholars. 

The 22nd Amendment to the Constitution states that "no person shall be elected to the office of the President more than twice."

But Trump said in March he was "not joking" about seeking a third term, adding without elaboration that there are "methods" that would allow it to happen.

Changing the Constitution to allow a third term would be a heavy lift, requiring a two-thirds majority in both houses of Congress and ratification by at least 38 of the 50 US state legislatures.

But "this is not something I'm looking to do," Trump told NBC's Welker, adding, "I'm looking to have four great years and turn it over to somebody, ideally a great Republican, a great Republican to carry it forward."

Asked who that might be, he mentioned Vice President JD Vance — calling him a "fantastic, brilliant guy" — and Secretary of State Marco Rubio, while adding that "we have a lot of good people in this party."