Washington (CNN) -- Federal workers nervously eyed the clock and an American public sharply divided along partisan lines watched from the sidelines Friday as Democrats and Republicans sniped at one another in a budget battle that could shut down the government and idle more than 800,000 people.
Negotiators have until midnight Friday to reach an agreement, or the government's massive gears will begin grinding to a halt.
Should the government shut down, operations from national parks to veterans' clinics would close. The White House visitor center would go dark. Even some government websites would blink out, replaced by virtual closed signs.
But not everything would close.
Essential services such as defense, air traffic control and law enforcement would continue largely unabated, as would Social Security enrollments and payments. The Social Security Administration said a backlog of applications would be crippling.
Medicare payments would also continue, as would health benefits for government employees. Electronically filed tax returns would be processed. And although paper returns wouldn't be reviewed, a shutdown wouldn't equal a tax holiday -- returns would still be due April 18.
The government estimates that 800,000 federal government employees would be sent home to anxiously await an agreement in what could become a lengthy, and unpaid, vacation. Even those who are asked to work wouldn't get paid until after the shutdown ends, and that could include U.S. troops fighting overseas.
But the president and members of Congress will continue to get paid, although Boehner, Democratic Sen. Joe Manchin of West Virginia and some others have said lawmakers should return their salaries should it come to that.
In the short term, a shutdown -- the first since 1996 -- would frustrate anyone who wants to go camping in a national park, get a passport to leave the country or receive a visa to come in.
It would probably also cost the government millions in shutdown costs, possible overtime pay to recover from the work that would pile up during a shutdown.
In the long term, a shutdown could, President Barack Obama warned, plunge the country's fragile economy back into recession.
The current debate also presages likely battles over raising the limit on how much money the federal government can borrow and the 2012 budget, said Norm Ornstein, a resident scholar at the conservative American Enterprise Institute.
Even if a compromise settlement avoids a shutdown, Tea Party supporters will probably feel the need to push even harder on the upcoming fiscal issues. His prediction?
"More end games, more threats, all year," he said.
In the here and now, everyday families -- people who depend on federal government paychecks and those who make use of federal services that would be shuttered -- fretted over how a shutdown would affect their lives.
"I live in one room to save heat, buy limited groceries and struggle to make ends meet," said Chris Cronkite of Bakersfield, California, who said her military contractor husband probably would be furloughed.
"There is a good chance I will be walking out of here with nothing if the money stops flowing," she said. "Basically, loading up the truck with the family photos and going camping."
It's not something Americans appear pleased to see happen. A majority of Americans -- 58% -- want congressional lawmakers to seek compromise to avoid a government shutdown, according to a Gallup poll released Wednesday.
Those numbers belie a sharp partisan divide on the issue, with 68% of Democrats favoring compromise, compared with 44% of Republicans.
But many Americans seemed tired of the bickering.
Austin Flor of Augusta, Georgia, implored members of Congress to "please stop acting like children and more like the leaders you were elected to be."
So how did it come to this?
When voters gave control of the House to Republicans -- including many backed by the fiscally conservative Tea Party -- in November, the GOP vowed that pushing spending cuts would be a major part of its agenda. With Democrats in charge of the Senate and the White House, the threat of a shutdown has loomed ever since.
Unable to reach a long-term agreement, Congress has since funded the government with a series of temporary spending measures called continuing resolutions. Congress approved the last one on March 17.
It is that measure that expires at midnight, leaving federal agencies with no money to continue operating.
This week, the House passed a bill to continue government operations for a week, cut $12 billion from the budget and fund military operations through the end of the year.
Obama said he would veto the bill even if the Democrat-controlled Senate passed it.
Congressional Republicans, who want to cut $61 billion, say getting spending under control with what would probably be the largest single-year budget cuts ever is critical for the economy's long-term health.
"When will the White House and when will Senate Democrats get serious about cutting spending?" Boehner said Friday.
Democrats say the stalemate isn't about spending, although they have suggested cutting $33 billion. Senate Majority Leader Harry Reid, D-Nevada, said it's about an "extreme agenda" to strip funding from Planned Parenthood and other organizations linked to abortion.
But some Americans painted the threat of a shutdown in less ideological terms.
Scott Maxwell was chaperoning an eighth-grade class from Mission Viejo Christian School in California on a Friday visit to Statue of Liberty in New York.
If the government shuts down, his could be one of the last groups to visit the American icon for who knows how long.
"I'm glad we're here today," he said.
The immediate concern is whether the next scheduled paycheck includes only one week's pay instead of two. 'If this goes on too long, I'm going to be hurting big time,' one Marine says. 'So are a lot of guys.'
Few Marines could be found dining at Davina's Cabo Grill and Cantina, or the Rice Garden, or Johnny Manana's. A handful shopped at T-shirt stands or jewelry stores, or sipped beer at favorite hangouts.
Even the line at Regal Cinemas was shorter than usual — though the Marine-centric "Battle: L.A." was playing. The pizza parlor next door was deserted.
For weeks, various commands have been warning Marines on the sprawling San Diego County base that a day of reckoning was coming. Now that day has arrived and Marines appear to be reacting by staying on base, satisfying themselves with chow hall fare and maybe a video rental.
If Republicans and Democrats fail to negotiate a compromise over federal spending reductions, a government shutdown will commence after midnight Friday. Should that happen, military personnel would continue to earn money but would not receive paychecks until Congress appropriated the money.
Defense officials have said that operations in Afghanistan, Iraq, Libya, Japan and elsewhere would not be affected, nor would training for upcoming deployments. The immediate concern is whether scheduled military paychecks April 15 would include only one week's pay instead of two.
So much of the talk among Marines on this weeknight was not about deployments or new physical fitness rules but about the possible government shutdown and what it would mean for them.
"I've got a mortgage back home in Kansas, and gas and food to buy," said Lance Cpl. Tim Hartman, 29. "If this goes on too long, I'm going to be hurting big time. So are a lot of guys."
At the Dairy Queen, Sgt. Marcus Johnson, 32, who was enjoying chili dogs and ice cream with his wife and their three children, said he's been preparing for a shutdown.
"My finances are in order. We're going to be fine," he said. "We don't live paycheck to paycheck."
Sgt. Joshua Gilbert, 25, also with a wife and three children, said he too would be able to get through a short-term financial squeeze.
"But I'll bet 90% of the privates and corporals are going to be in trouble," Gilbert said. "The young guys tend to get paid, spend it all and then wait for the next paycheck."
At Cabo Grill, some of the strongest comments came from Marine wives unwilling to be quoted by name. Military law makes it a crime to criticize the commander-in-chief, even for his role in a budget fight.
"If they're not going to pay the military, to turn their back on the guys defending this country, then they're going have trouble" recruiting, a sergeant's wife fumed. "I'll personally tell the C.O. that he can…."
Her rant was cut short when her husband told her to "be quiet. Right now."
The wife of a gunnery sergeant, who has made seven deployments in his 16 years, said a possible shutdown is a major topic when spouses congregate on base.
"We're all talking about it," she said. "I've lost sleep over it. They shouldn't treat us like this. Nobody should be treated like this."
Sen. Kay Bailey Hutchison (R-Texas) on Wednesday introduced the Ensuring Pay of Our Military Act of 2011 to make sure military personnel would continue to be paid. But the bill will have to clear several hurdles.
Cpl. Sam Rydzynski, 22, out for a stroll with his wife, Samantha, 21, said he refuses to worry about the situation. He noted that there are funds on base for Marines and sailors who find themselves short of cash.
"We'll get through it," he said. "That's what Marines do: They get through tough times."
On Thursday, the House of Representatives passed a spending measure that would fund the Department of Defense through September and also keep the government open for an additional week. But President Obama has threatened to veto the measure in a continuing dispute over spending priorities.