Trump downplays moment as impeachment hearings open

US president Donald Trump said he was "too busy" doing the people's business to watch the impeachment hearings that imperil his presidency.

But even as Mr Trump tried to suggest he was above the fray, the president tweeted two dozen times before noon laying out his grievances about the process playing out on the opposite end of Pennsylvania Avenue in Washington.

And Mr Trump could not resist taking a swipe at one of his political foes as he sat next to another world leader in the Oval Office.

"It's a witch hunt, it's a hoax, I'm too busy to watch it," Mr Trump told reporters.

"There's nothing there. I see they're using lawyers that are television lawyers, they took some guys off television. You know, I'm not surprised to see it, because Schiff can't do his own questions."

That was a reference to Adam Schiff, the House intelligence committee chairman overseeing the impeachment hearings on Capitol Hill.

The public impeachment hearings began on Wednesday with two career public servants raising their hands and swearing an oath to the truth, not the presidency, representing an integral part of the system of checks and balances envisioned by the Founding Fathers.

Mr Trump has pushed back vigorously on the impeachment inquiry, insisting he did nothing wrong in his dealings with Ukraine.

"New hoax. Same swamp," read one tweet from the White House that Mr Trump retweeted as the proceedings began.

He quoted his defenders and lashed out at the first witnesses to testify publicly, declaring William Taylor, the charge d'affaires in Ukraine, and George Kent, a career diplomat, as "NEVER TRUMPERS!"

Mr Taylor and Mr Kent worked for Republican and Democratic administrations. There is no evidence that either engaged in partisan activity opposing Mr Trump.

Overall, the president tweeted or retweeted more than 24 times before sitting down with Turkey's Recep Tayyip Erdogan, circulating a video in which Mr Trump deemed the impeachment proceedings "the single greatest scam in the history of American politics".

"Our country is at stake like never before," Mr Trump said in the video. "They're trying to stop me, because I'm fighting for you. And I'll never let that happen."