Trump's address to Congress on Tuesday made repeated appeals to optimism and the spirit of cooperation.

Although he goaded opposition Democrats by lashing out against "socialism" and insisting, as ever, on his controversial US-Mexico wall project, he spent much of the speech in unusually compromising mode.

At least, until around lunchtime Wednesday.

Asked by reporters about the Democrat-led intelligence committee in the House of Representatives expanding a probe into his Russia connections, Trump reverted to his habit of name calling.

He labelled Adam Schiff, the chairman of the committee, "a political hack who's trying to build a name for himself."

Schiff has been a frequent target of Trump, who has referred to him on Twitter as "Schitt" and "Little Adam Schitt."

'Right to know' 

Trump was infuriated by Schiff's decision to boost an already sensitive look by the committee at Trump's dealings with Russia.

Schiff said that the committee wanted to know whether "any foreign actor has sought to compromise or holds leverage, financial or otherwise, over Donald Trump, his family, his business, or his associates."

"The American people have a right to know," Schiff said.

Trump said he is being victimized.

"There would be no reason to do that. No other politician has to go through that. It's called presidential harassment and it's unfortunate," he told reporters at the White House. "It really does hurt our country."

The intelligence committee's investigation will run parallel to a major existing probe run by special prosecutor Robert Mueller into explosive allegations that Russian agents colluded with Trump in his 2016 election campaign.

Trump says he has only had legitimate links with Russian real estate and other partners, calling Mueller's efforts a "witch hunt."

But the subject needles him and is set to become ever more intrusive, with Mueller believed to be finalizing a report on his findings, Democrats mounting their own probes, and federal prosecutors in New York targeting yet more allegations. 

In his State of the Union speech, Trump mentioned the probes only briefly, but emphatically, claiming the "ridiculous partisan investigations" pose as much danger to the US economy as wars in places like Afghanistan.

Vice President Mike Pence drove home the idea on Wednesday, telling CBS television: "We don't object to oversight. That's the proper role of committees in the Congress. But when it takes on a partisan tint..., more intent on becoming a forum for invective against the president and against the administration, the American people expect better."

But Chuck Schumer, the senior Democrat in the Senate, accused Trump of trying to intimidate Congress.

"The president says if you investigate me I'm not going to make progress," Schumer told CNN, accusing Trump of "holding the American people hostage."

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