But people classified as essential government employees — such as air traffic controllers, Border Patrol agents and most food inspectors — will continue to work. So will members of the military and employees whose jobs are financed through fees, such as State Department workers who issue passports and visas.
With the Republican-controlled House and Democratic-controlled Senate stalemated, it was unclear how long the shutdown — and the loss of some government programs and services — could last. The Senate early Tuesday rejected the House's call to form a negotiating committee to resolve the deadlock.
Moments after the vote, Senate Majority Leader Harry Reid, D-Nev., laid full blame on House Republicans, declaring, "The government is closed because of the irrationality of what's going on on the other side of the Capitol."
But Republican Sen. John Cornyn of Texas said GOP lawmakers were listening to constituents who want to "stop the runaway train called the federal government." Their message, he said, is "Stay strong."
Obama communications director Jennifer Palmieri told MSNBC that the White House was open to changes in the health care law in future negotiations, but not as part of passing a budget bill. She compared that to negotiating with "a gun pointed to your head."
Obama was meeting with citizens signing up for his health care program on the opening day of enrollment. Then he planned to make a statement about the shutdown in a lunch-hour speech in the Rose Garden.
In the House, conservative Rep. Marsha Blackburn predicted the standoff might drag on for days if Obama and Senate Democrats refused to bargain. "People are going to realize they can live with a lot less government," Blackburn, R-Tenn., told Fox News.
Another Republican, Rep. Scott Rigell of Virginia, whose Norfolk-area district includes tens of thousands of military members and their families, tweeted "We fought the good fight. Time for a clean CR" — referring to a continuing resolution that would reopen the government without addressing health care.
The health care law itself was unaffected Tuesday as enrollment opened for millions of people shopping for medical insurance.
It was the first shutdown since a budget battle between Republicans in Congress and Democratic President Bill Clinton in the winter of 1995-1996.
Congress itself was affected. Some staffers were furloughed and hearings were postponed. The U.S. Capitol canceled tours not personally led by lawmakers. Democratic Sen. Tom Carper sent an email to his Delaware constituents telling them not to expect responses to their emails and phone calls.
Lawmakers and the president were still getting paid, however, at a rate totaling more than $250,000 per day. Most of the nation's 2.1 million civilian federal workers were either working with their pay suspended or on unpaid furlough.
The Supreme Court operated as usual, even welcoming tour groups, but was at risk of running low on money if the shutdown lingers beyond Friday.
Tourists were left with few other government options. The Smithsonian website displayed a red banner noting that "all Smithsonian museums and the National Zoo are closed." On the zoo's website, panda mom Mei Xiang could be seen snuggling with her weeks-old cub through the morning, until the feed was abruptly cut off around 8 a.m. Care of the animals will continue behind the scenes.