As many as one million people flooded into Washington for a massive rally organised by conservatives claiming that President Obama is driving America towards socialism.
The size of the crowd - by far the biggest protest since the president took office in January - shocked the White House.
Demonstrators massed outside Capitol Hill after marching down Pennsylvania Avenue waving placards and chanting 'Enough, enough'.
Tens of thousands of people converged on Capitol Hill on Saturday to protest against government spending
The focus of much of the anger was the president's so-called 'Obamacare' plan to overhaul the U.S. health system.
Demonstrators waved U.S. flags and held signs reading 'Go Green Recycle Congress' and 'I'm Not Your ATM'.'
The protest on Saturday came as Mr Obama took his campaign for health reforms on the road, making his argument to a rally of 15,000 supporters in Minneapolis.
Saying he was determined to push through a bill making health insurance more affordable, Mr Obama said: 'I intend to be president for a while and once this bill passes, I own it.
'I will not waste time with those who think that it's just good politics to kill healthcare.'
But in Washington, protester Richard Brigle, 57, a Vietnam veteran, said: 'It's going to cost too much money we don't have.' Another marcher shouted: 'You want socialism? Go to Russia!'
Terri Hall, 45, of Florida, said she felt compelled to become political for the first time this year because she was upset by government spending.
'Our government has lost sight of the powers they were granted,' she said. She added that the deficit spending was out of control, and said she thought it was putting the country at risk.
Anna Hayes, 58, a nurse from Fairfax County, stood on the Mall in 1981 for Reagan's inauguration. 'The same people were celebrating freedom,' she said. 'The president was fighting for the people then. I remember those years very well and fondly.'
Saying she was worried about 'Obamacare,' Hayes explained: 'This is the first rally I've been to that demonstrates against something, the first in my life. I just couldn't stay home anymore.'
Andrew Moylan, of the National Taxpayers Union, received a roar of approval after he told protesters: 'Hell hath no fury like a taxpayer ignored.'
Republican lawmakers also supported the rally.
'Republicans, Democrats and independents are stepping up and demanding we put our fiscal house in order,' Rep. Mike Pence, chairman of the House Republican Conference, said.
'I think the overriding message after years of borrowing, spending and bailouts is enough is enough.'
FreedomWorks Foundation, a conservative organization led by former House of Representatives Majority Leader Dick Armey, organized several groups from across the country for what they billed as a 'March on Washington.'
Organisers said they had built on momentum from the April 'tea party' demonstrations held nationwide to protest at Mr Obama's taxation policies, along with growing resentment over his economic stimulus packages and bank bailouts.
Other sponsors of the rally include the Heartland Institute, Americans for Tax Reform and the Ayn Rand Center for Individuals Rights.
Recent polls illustrate how difficult recent weeks have been for a president who, besides tackling health care, has been battling to end a devastatingly deep recession.
Fifty per cent approve and 49 per cent disapprove of the overall job he is doing as president, compared to July, when those approving his performance clearly outnumbered those who were unhappy with it, 55 per cent to 42 per cent.
Just 42 percent approve of the president's work on the high-profile health issue.
The poll was taken over five days just before Obama's speech to Congress. That speech reflected Obama's determination to push ahead despite growing obstacles.
Prior to Obama's speech before Congress U.S. Capitol Police arrested a man they say tried to get into a secure area near the Capitol with a gun in his car as President Barack Obama was speaking.
On Thursday police spokeswoman Kimberly Schneider said that 28-year-old Joshua Bowman of suburban Falls Church, Virginia, was arrested around 8pm on Wednesday when Obama was due to speak.
Please write: COMMENT in this box to verify that you are human