The supercommittee pulls the trigger: How do the automatic cuts work?

It's all over. The "supercommittee"--the bipartisan group of lawmakers charged with hammering out a plan to reduce the federal deficit--has admitted defeat. With the panel's Wednesday deadline looming, Democrats and Republicans say they're just too far apart on what mix of tax hikes and spending cuts would be best.

Under the terms of the law that created the supercommittee this summer, a stalemate triggers automatic spending cuts of $1.2 trillion, the amount of deficit reduction the panel was tasked with achieving. The idea was that those automatic cuts would be so unpopular that they would create an incentive for the supercommittee to come to a deal.

So much for that plan. So what happens now?

Where will the automatic spending cuts come from?

By law, 18 percent of the savings--or $216 billion--is assumed to come from reduced interest payments. So that leaves $984 billion in actual cuts, divided equally between defense and domestic programs.

When would they go into effect?

The cuts are supposed to start in 2013 and would be spread across the next nine years. That means that both defense and domestic programs would each see cuts of around $55 billion a year for that period.

That sounds like a lot. What are the implications for national security?

There's disagreement on just how damaging the defense cuts would be. Defense Secretary Leon Panetta has said they would require a 23 percent reduction of the military's budget for 2013, forcing civilian employees to be furloughed and threatening combat readiness.

"Facing such large reductions, we would have to reduce the size of the military sharply," Panetta wrote in a letter to lawmakers last week, in which he invoked a "doomsday" scenario. And Buck McKeon, a Republican representative from California who chairs the House Armed Services Committee, wrote to the supercommittee recently that "unless we act today, the dismantling of the greatest armed forces in history could begin tomorrow."

Many others say those dire warnings are overblown. Lawmakers from both parties have been looking to reduce the Pentagon's bloated budget anyway, so the Defense Department is already preparing for around $450 billion in cuts over the next decade. If the automatic cuts also go into effect, defense spending would fall by about 11 percent to around $472 billion in 2013--about the same level it was at in 2007, according to defense budget experts. (From there until the end of the decade, the defense budget would grow with inflation.)

Many others say those dire warnings are overblown. If the automatic cuts go into effect, defense spending would fall by about $490 billion--or around 11 percent--over the next decade. In 2013 alone, the United States would still spend around $472 billion on defense. That's the amount we spent in 2007, according to defense budget experts. We could cut even deeper, to a budget of around $425 billion annually, and still spend more than four times the amount budgeted by our closest competitor, China.

"The range of cuts being discussed is still well within the proportions of drawdowns after the ends of the Korean, Vietnam and Cold wars," Aviation Week wrote recently. "Even the most drastic cuts will not end the U.S.'s superpower status."

The real problem may have less to do with the size of the cuts than with how they're likely to happen. At least at the start, the cuts will go into effect in a mechanical, across-the-board fashion, without regard to larger strategic considerations--an approach that just about everyone agrees is the worst possible way to reduce defense spending.

"Strategy needs to drive budgets, and not the other way around," Michael Breen, a vice president of the Truman National Security Project and a decorated former Army captain, told Yahoo News. "The idea that some self-imposed political crisis dictates our national-security strategy is insane."

What about on the domestic front?

Grandma can relax, mostly. Social Security is exempt from the automatic cuts under the trigger scenario. And Medicare cuts, which are limited to 2 percent of that program's budget, will come from reductions in payments to doctors and hospitals, not from cuts to seniors' benefits. Also exempt are several programs that benefit the poor--unemployment insurance, Medicaid, and food stamps, among others--as well as those that benefit veterans.

What does that leave? Several other programs that play a key role in the social safety net--low-income housing vouchers; the Head Start early education program; and public health initiatives, for instance--are likely to be on the chopping block, according to Richard Kogan, a senior fellow at the liberal Center on Budget and Policy Priorities and a former White House budget adviser.

There's also the rest of the domestic spending landscape: the Environmental Protection Agency, the National Institutes of Health, NASA, the National Parks, and so on.

As with defense, the cuts will at first be applied uniformly and indiscriminately. "Whatever those programs would otherwise have gotten in 2013, they're gonna get 9.3 percent less," Kogan told Yahoo News, citing the figure by which domestic spending will be reduced under the trigger.

Are these cuts definitely going to happen?

Not necessarily. Lawmakers opposed to the cuts have more than a year to pass legislation that would eliminate the trigger, and some Republicans, concerned about the cuts to the military budget, are already pushing a bill that would stop them from taking effect.

Yet the automatic trigger was approved by Congress just a few months ago, and the White House has said that President Obama would veto any measures to override it. Speaker of the House John Boehner has said he'd feel "bound" to honor the trigger. It's unclear whether those pledges have any wiggle room.

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