Republican Sens. Ted Cruz of Texas and Mike Lee of Utah, along with former Alaska Gov. Sarah Palin, were part of the demonstrators.
Cruz and Lee are among the tea party-backed lawmakers who refused to keep the government operating unless President Barack Obama agreed to defund the nation's health care overhaul.
"Let me ask a simple question," Cruz told the crowd of hundreds that gathered beginning at 9 a.m. "Why is the federal government spending money to erect barricades to keep veterans out of this memorial?"
Black metal barricades have lined the front of the memorial since the government closed Oct. 1. That's when more than 300 National Park Service workers who staff and maintain the National Mall were furloughed.
As the crowd entered the memorial plaza, they chanted "Tear down these walls" and "You work for us." They sang "God bless America" and other songs.
"Our vets have proven that they have not been timid, so we will not be timid in calling out any who would use our military, our vets, as pawns in a political game," Palin told the crowd.
The memorial has become a political symbol in the bitter fight between Democrats and Republicans over who is to blame for the shutdown. Earlier rallies have focused on allowing access for World War II veterans visiting from across the country.
Sunday's rally was more political. A protest by truckers converged with a rally by a group called the Million Vet March at the memorial. Participants cut the plastic links between metal barriers at the National Park Service site and pushed them aside.
Later, some protesters carried metal barricades that look like bicycle racks from the memorial to the White House and stacked them up outside the gates, confronting police in riot gear. Some protesters carried signs reading "Impeach Obama."
Police moved the protesters back to set up barricades between the crowd and the White House gate. Some protesters chanted "shame on you" at the officers.
An armored police vehicle also was sent to the World War II Memorial as people lingered there.
District of Columbia police said the crowd was dispersing by 1 p.m., about four hours after the protests began. U.S. Park Police said there had been one arrest at the Lincoln Memorial for assault, but it was not related to the protest, said Lt. Pamela Smith.
Jim Weller of Allentown, Pa., said he came to protest "to stand up for my rights."
"My father was a World War II veteran, shot down in the Philippines in 1945, and for them to shut down this memorial is absurd," he said.
Cindy Good had a message for lawmakers.
"They need to listen to the American people," she said, "and try to work together in Congress to get this whole thing worked out."
After the protest, U.S. Park Police worked to secure the World War II Memorial again, and Smith said they were still closed because of the shutdown.
The Park Police officers, who have been guarding the memorials amid protests over their closure, are not being paid during the government shutdown.
Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.