"The people understand it's a scam," he said and accused Democrats of trying to win the 2020 election by impeaching him.

Syria move shocks the world

Trump's disruptive mood stretched beyond US borders on Monday into a military conflict that is every bit as intractable as his showdown with Democrats.

"I urge the President to exercise American leadership to keep together our multinational coalition to defeat ISIS and prevent significant conflict between our NATO ally Turkey and our local Syrian counter-terrorism partners," said Senate Majority Leader Mitch McConnell, a Republican from Kentucky.

A cynic might suggest that the GOP lawmakers were embracing a chance to criticize the President on an issue that is hardly a critical one for conservative voters while avoiding accusations that he abuses his power in his dealings with Ukraine.

Any Republican lawmaker who wants to have a serious political career in the years ahead cannot afford to anger the all-powerful Trump base, especially those who fear primary challenges as they seek reelection.

Dems' impeachment inquiry takes next steps

The Democrats' impeachment investigation is grinding relentlessly onward. On Tuesday, US Ambassador to the European Union Gordon Sondland is due to give a closed-door deposition and will become the latest official or witness to the President's dealings with Ukraine to tell his story.

The President complained on Monday that the Democratic investigation was making it impossible to do his job. But his belligerence and unrestrained conduct in reality is making it hard for Congress to fulfill its constitutional role.

The House Intelligence Committee is discussing extraordinary measures to protect the identity of the whistleblower who set off the impeachment circus by accusing Trump of pressuring Ukraine's President to investigate Biden in a call.

Among possible measures are the use of an off-site location for any testimony — potentially including highly secure sites at the CIA or at Fort Meade base outside Washington, the home of US Cyber Command. There could also be limits on the number of Capitol Hill staff and members who could attend and the voice of the yet-to-be named whistleblower could be disguised.

That such measures are needed is unusual in itself. What makes this scenario stunning is that they are being discussed as a direct result of threats made by the President. Trump demanded to meet his "accuser," suggested the person was "spying on the US President" and appeared to suggest the whistleblower's sources should be executed like "in the old days."

Lawyers for the whistleblower warned last week that their client was in danger. There is so far no agreement for he or she to testify but talks are continuing.

"We cannot allow the President to somehow get to the whistleblower, or threaten him or discourage him or her form telling their side of the story," Illinois Democratic Rep Raja Krishnamoorthi said on CNN's "The Situation Room."

The measures that could be taken to protect the whistleblower are also a commentary on the bitter schism between Republicans and Democrats on the House Intelligence Committee. The unstated fear of Democrats is that some of Trump's close allies on the Intelligence panel could reveal the name of the whistleblower to the White House if the person is identified. Republicans meanwhile may seize on extreme precautions by Democrats to suggest they are deepening antagonism between the parties in a symptom of what the GOP says is a partisan impeachment process.

Sondland to testify

In the next stage of the proceedings Tuesday, Sondland is expected to testify to three House committees.

The ambassador is mentioned in a series of text messages between US diplomats and a Ukrainian aide.

The President on Monday notably failed to leap on an out offered to him by Republicans who suggested he was joking when he called on China — on the White House South Lawn last week — to open an investigation into Biden, his possible 2020 election opponent. The President's agitated demeanor and his willingness to use the symbolism of his office for such an extraordinary purpose seemed more sinister than humorous at the time.

But House Republican Minority Leader Kevin McCarthy, Florida Sen. Marco Rubio and Missouri Sen. Roy Blunt all suggested recently that the media took Trump too literally.

A stone faced President refused to answer repeated questions about such comments at the White House on Monday evening.

"It's a coup," read an email from the Trump/Pence campaign. "Democrats are trying to undo the Election regardless of the FACTS!"

Alongside the Republican National Committee, the campaign held a conference call featuring officials who hit White House talking points, discredited national polling on impeachment, and touted ad buys and new donors as proof Democrats are heading down the wrong path.