A defiant rejection of his massive social spending bill by a single US senator -- a fellow Democrat -- and a surge in Covid cases are imperiling Joe Biden less than a year into his presidency.

Returning to the White House from a weekend at his family home in Delaware, the 79-year-old president, wearing a black face mask, headed straight from his helicopter to the Oval Office without a word or a glance at a scrum of waiting reporters.

West Virginia Senator Joe Manchin dealt a potentially fatal blow this weekend to Biden's $1.75 trillion "Build Back Better" plan designed to equip the United States to face 21st Century challenges such as climate change and Chinese competition.

The president has not publicly responded to Manchin's body blow, confining himself to a single tweet.

US President Joe Biden returns to the White House after spending the weekend in Wilmington, Delaware
US President Joe Biden returns to the White House after spending the weekend in Wilmington, Delaware GETTY IMAGES via AFP / Drew Angerer

"Right now, there's a kid out there whose family can't afford her insulin because it costs $1,000 per month," Biden tweeted on Monday. "The Build Back Better Act would cap their monthly insulin costs at $35. I'm committed as ever to getting it done for them."

Democratic Senate Majority Leader Chuck Schumer sought to rally his demoralized troops, pledging to bring the bill -- the centerpiece of Biden's domestic agenda -- to the Senate floor.

"We are going to vote on a revised version of the House-passed Build Back Better Act -- and we will keep voting on it until we get something done," Schumer said.

How they could do so without the crucial vote of the senator from West Virginia in an evenly divided Senate is not clear.

US President Joe Biden salutes as he exits Marine One on the South Lawn of the White House
The White House staffer is fully vaccinated and has had a booster shot. In photo: US President Joe Biden salutes as he exits Marine One on the South Lawn of the White House. GETTY IMAGES via AFP / Drew Angerer

Manchin announced on Sunday on Fox News, former Republican president Donald Trump's favored TV network, that he was a "no" on the bill that proposes sweeping reforms to health care, immigration, climate and education.

Republican senators who backed the president's infrastructure bill have also made it clear that they will not support Build Back Better, which they claim would push the United States down a path to "socialism."

White House Press Secretary Jen Psaki issued a blistering statement blasting Manchin's "breach of his commitments to the president" and the "sudden and inexplicable reversal in his position."

With his popularity ratings already mired in the low 40s, Biden's political capital is at a low ebb less than a year ahead of mid-term elections that could well see Democrats lose control of both chambers of Congress.

As a former senator who considers himself a master of the legislative game, Biden personally invested in trying to get Manchin on board, to the chagrin of some members of the progressive wing of the Democratic Party.

Democratic Senator Joe Manchin of West Virginia
Democratic Senator Joe Manchin of West Virginia GETTY IMAGES NORTH AMERICA via AFP / Anna Moneymaker

"It's really about time that we take the kid gloves off and we start using them to govern for working families in this country," Representative Alexandria Ocasio-Cortez, one of the leading figures in the left wing of the party, said on MSNBC.

As powerless as Biden appeared to be in facing down a senator who represents a tiny state of just 1.7 million people, he has appeared equally helpless against the new wave of Covid cases in a country which has already seen more than 800,000 deaths from the disease.

Biden is to deliver a speech on Covid on Tuesday and Psaki said he does not plan on "locking the country down" in response to the surge in coronavirus cases.

"This is not a speech about locking the country down," Psaki told reporters.

"This is a speech outlining and being direct and clear with the American people about the benefits of being vaccinated, the steps we're going to take to increase access and to increase testing."

Top US pandemic advisor Anthony Fauci warned on Sunday of a bleak winter ahead as the Omicron coronavirus variant spurs a new wave of infections globally.

"With Omicron," Fauci told NBC News, "it is going to be a tough few weeks to months as we get deeper into the winter."

While a little more than 70 percent of the US population has had at least one shot, according to the US Centers for Disease Control and Prevention, another 50 million eligible people remain unprotected, Fauci said.

Hospitals are getting busy, testing centers are seeing long lines, and sports and entertainment events are being cancelled in what adds up to a disaster for Biden, who was elected on promises to defeat the virus and protect Americans after the mixed messages of Donald Trump.

But getting the virus under control has proved difficult in a country where vaccination and mask-wearing have become divisive political issues, and federal mandates end up in protracted legal battles.

Biden has attempted to impose vaccine mandates on private businesses and federal employees but has resorted in recent weeks to little more than publicly beseeching people to get their shots.