The debate ranged widely, from Iran's threat to develop a nuclear weapon to the anti-terror Patriot Act, the war in Afghanistan, U.S-Pakistan relations and illegal immigrants who have entered the U.S. across the Mexican border. Former House Speaker Newt Gingrich said some should be allowed to stay, drawing fire from rivals Mitt Romney and Michele Bachman.
On defense spending, former Massachusetts Gov. Romney said nearly $1 trillion in cuts are on the horizon for the Pentagon over the next decade, noting that is the same as the costs for the nation's new health care law. He blamed Obama for that, adding, "We need to protect America and protect our troops and our military and stop the idea of Obamacare."
Texas Gov. Rick Perry was harshly critical of the magnitude of potential cuts saying the Obama administration's Pentagon chief had called them irresponsible. "If Leon Panetta is an honorable man, he should resign in protest," Perry said.
Neither Perry nor Romney specified if they support any cuts in the Pentagon's accounts, but Gingrich and Jon Huntsman, one-time ambassador to China, both indicated the topic should be on the table as budget-cutters look for savings.
"It's clear that there are some things you can do to defense that are less expensive," said Gingrich.
Only Rep. Ron Paul of Texas sounded unperturbed, saying that despite ominous talk, lawmakers are considering only reductions in future military growth, not actual cuts.
In a race constantly in flux, the former House speaker has recently emerged as Romney's principal rival atop the public opinion polls. As he looked around him, he saw other rivals who once held that position - Bachmann, Perry and businessman Herman Cain among them.
They and the other GOP would-be commanders-in-chief made their points in a national security debate a mere six weeks before the Iowa caucuses begin the formal competition for delegates to next summer's National Republican Convention. The venerable DAR Constitution Hall was the site - a few blocks from the White House and as close as most if not all of the GOP hopefuls are likely to get.
On immigration, Gingrich said that while some who are in the country illegally should be forced to leave the country, that wasn't true for all of them.
"If you've been here 25 years and you got three kids and two grandkids, you've been paying taxes and obeying the law, you belong to a local church, I don't think we're going to separate you from your family, uproot you forcefully and kick you out," he said.
Romney and Minnesota Rep. Bachmann strongly differed. She said, "I don't agree that you would make 11 million workers legal, because that, in effect is amnesty."
Neither the format nor the moderator permitted all eight candidates to answer any one question, producing a somewhat disjoined event in which there was relatively little back-and-forth among the rivals.
Syria was one exception - Perry saying he supported a no-fly zone over the nation where President Bashir Assad's forces are using force to quell protests, and Romney saying now is not the time.
The focus on defense cuts came one day after Congress' supercommittee failed to reach agreement on a plan to reduce red ink by $1.2 trillion over the next decade, an outcome that threatens to trigger a similar amount in automatic spending cuts beginning in 2013.
The Pentagon's share of those reductions would be about $500 billion, an amount that would come on top of Obama's own plan to trim military costs by about $450 billion.
Romney did not distinguish between the two categories when he accused Obama of targeting the Pentagon for debilitating reductions.
"They're cutting a trillion out of the defense budget, which just happens to equal the trillion dollars that they're putting into Obamacare," he said. He said such a Pentagon reduction would crimp weapons acquisition and other critical defense needs.
Several Republicans spoke up strongly for the anti-terror Patriot Act, saying it should be extended or perhaps strengthened to help identify and capture those who would attack the United States.
Only Rep. Paul among the eight presidential hopefuls dissented, arguing that the law is "unpatriotic because it undermines our liberties."
Gingrich jumped at that. "That's the whole point. Timothy McVeigh killed a lot of Americans," the former House speaker said. "I don't want a law that says after we lose a major American city, we're sure going to come and find you. I want a law that says, you try to take out an American city, we're going to stop you."
Neither Gingrich nor any other Republican mentioned that Obama, like President George W. Bush before him, signed legislation extending the Patriot Act. He did so while traveling in Europe last May, putting him name on a four-year extension of the law that gives the government sweeping powers to search records and conduct wiretaps in pursuit of terrorists.
Asked about the same general topic, Bachmann said Obama has "essentially handed over our investigation of terrorists to the" American Civil Liberties Union. "Our CIA has no ability to investigate," she said. Bachmann did not cite any examples to buttress either of her claims.
On other issues, Cain seemed to sidestep when asked if he would help Israel attack Iran in the event the Islamic regime acquired nuclear weapons. He said he would want to know what the plan was and have an understanding of its chance of success.
Gingrich said he would bomb Iran only as a last resort and with a goal of bringing about the downfall of the government.
There was disagreement when it came to the war in Afghanistan. Former Utah Gov. Huntsman said it was time for the United States to withdraw nearly all its troops.
Romney said top generals disagreed with that and asked Huntsman if he was talking about a withdrawal beginning immediately.
"Did you hear what I said?" Huntsman asked across the debate stage, noting that under the Constitution the president is commander in chief. A few moments later, referring to Vietnam, he said a president had listened to the generals in 1967, and the outcome was not in the interests of the United States.