Other signs did not focus on Mr. Obama, but rather on the government at large, promoting gun rights, tallying the national deficit and deploring illegal immigrants living in the United States.

Still, many demonstrators expressed their views without a hint of rage. They said the size of the crowd illustrated that their views were shared by a broader audience.

Image Protesters in Washington D.C. during a rally on Saturday. Credit... Amanda Lucidon for The New York Times

“I want Congress to be afraid,” said Keldon Clapp, 45, an unemployed marketing representative who recently moved to Tennessee from Connecticut after losing his job. “Like everyone else here, I want them to know that we’re watching what they’re doing. And they do work for us.”

As Mr. Obama traveled to Minnesota on Saturday to rally support for his health care plan, he flew over the assembling crowd in Marine One. The helicopter could be seen flying overhead as the demonstrators marched down Pennsylvania Avenue.

“This is not some kind of radical right-wing group,” Senator Jim DeMint, Republican of South Carolina, said in an interview as dozens of people streamed by him. “I just hope the Congress, the Senate and the president recognize that people are afraid of what’s going on.”

Mr. DeMint and a few Republican legislators were the only party leaders on hand for the demonstration. Republican officials said privately that they were pleased by the turnout but wary of the anger directed at all politicians. And most of those who turned out were not likely to have been Obama voters anyway.