The stalemate happened because Congress failed to pass any of the annual laws, known as appropriations, that provide money for government agencies. Federal law says agencies cannot spend money without an appropriation except when necessary to protect life or property, or in cases of programs that have permanent sources of funds.
Widespread disruption of services probably will not occur for a while. Many basic government functions do not depend on annual spending bills. Social Security checks will go out as always, for example, as will payments under Medicare. Mail delivery will be unaffected. Courts, which have reserve funds that can last for some time, will still hear cases.
But as other government functions close, economists say, a prolonged shutdown will slow growth. A two-week standoff would shave about three-tenths of a percentage point off the current growth rate, projections indicate. Although not huge, that punch would sting in an economy expanding at less than 2% per year. A longer standoff would cut growth more.
The last time the government closed, during the Clinton administration, two shutdowns took place. One lasted five days; the other, affecting only part of the government, ran three weeks.
Who gets the political blame for a shutdown will have a big impact on how the standoff ends.
Nearly all Democratic strategists and many Republican ones think Democrats hold the upper hand in the current fight, indicating that Republicans would eventually have to yield. Polls so far have indicated that Americans are somewhat more likely to blame congressional Republicans than Obama for the stalemate, although the advantage Democrats have is much smaller than the one they enjoyed in the Clinton-era standoff.
A Washington Post-ABC News poll released Monday showed majorities of the public disapproving of the way all the major actors in the budget drama have handled their roles, but giving congressional Republicans the worst reviews. Obama got the approval of 41% and the disapproval of 50%. Congressional Republicans got just 26% approval and 63% disapproval; congressional Democrats, 34% approval and 56% disapproval.
Some conservative Republicans argue that Obamacare's unpopularity ultimately will give them an advantage. Although polls show the health law is unpopular, the same surveys show the public does not support shutting down the government to block it.
In a CNN/ORC poll also released Monday, for example, Americans said, 60% to 34%, that it was "more important" for Congress to pass "a budget agreement that would avoid a government shutdown" than to approve legislation "preventing major provisions in the new healthcare law from taking effect."
As several polls have shown, Democrats remain largely united behind Obama, but significant numbers of Republicans disapprove of their party's leaders. That has proved true in Congress as well. Relatively conservative Democrats, such as Sen. Joe Manchin III of West Virginia and Mark Pryor of Arkansas, have consistently voted with Reid during the current standoff. By contrast, divisions on the Republican side have been open and bitter and continued to plague the party Monday.
In closed-door meetings, some of the most conservative members objected to the leadership's plans on the grounds that the latest House proposal would delay only part of Obamacare — the requirement that individuals buy health insurance — rather than the entire law.
On the other side, a group of Republicans, mostly from Northeastern and Midwestern states, said they believed the GOP should drop its efforts to block Obamacare and simply approve a measure to keep government agencies open. The group failed to round up enough support to block the Republican leadership's plans on Monday, but it could become a factor if the standoff drags on.
The party's current strategy is "a dead end," said Rep. Peter T. King (R-N.Y.). "We're going to shut the government down, and, when all is said and done, we're going to get blamed for it.
"We have too many people who live in their own echo chamber."
Evan Halper, Kathleen Hennessey, David Lauter, Don Lee and Christi Parsons in the Washington bureau contributed to this report.