In the Capitol building itself, guards in full camouflage and carrying assault rifles assembled.
The US House of Representatives began its momentous vote Wednesday on impeaching President Donald Trump for a second time, on charges of "incitement of insurrection."
After hours of intense debate, a bipartisan majority of members is expected to impeach the president, who urged supporters last week to march on the US Capitol and "fight like hell," actions that Democrats say incited a mob to stage a violent and deadly uprising.
Shortly before the vote began, number two House Democrat Steny Hoyer urged lawmakers to "reject sedition, tyranny and insurrection" and vote to impeach Trump "for America, for our constitution, for democracy, for history.
Accused of stoking the mob assault on Congress on January 6, Trump broke his silence from the White House only to issue a brief statement insisting on his opposition to violence.
"In light of reports of more demonstrations, I urge that there must be no violence, no lawbreaking and no vandalism of any kind. That is not what I stand for," he said.
"I call on all Americans to help ease tensions and calm tempers. Thank You."
Reflecting that fear of upheaval, armed National Guards deployed across the capital and central streets were blocked to traffic.
In the Capitol building itself, guards in full camouflage and carrying assault rifles assembled, some of them grabbing naps early Wednesday under the ornate statues and historical paintings.
The expected vote, coming seven days ahead of Democrat Joe Biden's inauguration, would make Trump the first US president to have been impeached twice.
Trump's epic downfall was triggered by his speech to a crowd on the National Mall last week, telling them that Biden had stolen the presidential election and that they needed to march on Congress and show "strength."
Amped up on weeks of conspiracy theories pushed by Trump, the mob then stormed into the Capitol, fatally wounded one police officer, wrecked furniture and forced terrified lawmakers to hide, interrupting a ceremony to put the legal stamp on Biden's victory.
One protester was shot dead, and three other people died of "medical emergencies," bringing the toll to five.
House Speaker Nancy Pelosi told the chamber that Trump "must go."
"He is a clear and present danger to the nation that we all love," she said.
Earlier, Democratic lawmaker Ilhan Omar branded Trump a "tyrant," saying that "for us to able to survive as a functioning democracy there has to be accountability."
But Nancy Mace, a newly-elected Republican congresswoman said that while lawmakers "need to hold the president accountable," the speed of the impeachment "poses great questions about the constitutionality."
So far six Republicans in the House have declared they will join Democrats in backing impeachment. But the body's top Republican, Minority Leader Kevin McCarthy, said that while Trump deserves censure, hurriedly impeaching will "further divide this nation."
Trump ostracized
Trump, who has been stripped of his social media megaphones by Twitter and Facebook, and finds himself increasingly ostracized in the business world, is struggling to impose his message -- let alone any kind of resistance.
On a quick trip to Texas on Tuesday he visited the US-Mexico border wall, which he regards as one of his biggest achievements. But the short, low-energy speech he made there did nothing to recapture his rapidly sliding momentum.
His insistence during the trip that his infamous address to the crowd on January 6 had been "totally appropriate" and that he bore no blame also infuriated allies and opponents alike.
The main question now is to what extent former Republican allies in the Senate will turn on their party's figurehead. Last year, they acquitted Trump overwhelmingly after the House impeached him for abuse of office.
Powerful Republican Senate leader Mitch McConnell has made clear that there is no time before Trump's January 20 exit to hold an impeachment trial, with the Senate in recess until January 19.
However, according to The New York Times, McConnell signaled privately on Tuesday that he believes Trump did commit impeachable offenses and he welcomes the impeachment.
If confirmed, this would be a potentially fatal shift in the ground under Trump's feet.
Although US media reported that McConnell has now ruled out calling back the Senate for an emergency session in the next few days, his general backing for impeachment could open the doors to other Republican senators convicting Trump after Biden assumes office.
Meanwhile, the increasingly toothless Trump's social media woes deepened late Tuesday when video-sharing giant YouTube said it was suspending his official account for at least a week, out of concern his videos could incite violence.
He is also being cut out by the business world, threatening his financial future once he leaves the White House.
The latest blow to the Trump empire was when the mayor of his native New York City, Bill de Blasio, announced Wednesday a termination of contracts to run a golf course, two ice-skating rinks and a carousel in Central Park.
"New York City doesn't do business with insurrectionists," de Blasio, a Democrat, tweeted.
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)