The debt deal painstakingly hammered out by Congress may vindicate a prediction repeated often by Adm. Mike Mullen, the departing chairman of the Joint Chiefs of Staff, in which he warns that "the most significant threat to our national security is our debt."

He is not talking about the risk of investors fleeing, but about the likelihood that cost-cutting zeal will extend to the military's budget. If the debt deal reached Sunday is any indication, his words may prove to be prescient.

Nearly half of the initial $900 billion in cuts laid out in the compromise will come from "security spending," a category that includes defense and homeland security. The second round of mandated deficit reduction contains a provision that, if Congress does not pass a measure to reduce the deficit, would automatically level deep cuts in defense spending and domestic spending.

The trigger is intended as a way to ensure that Democrats and Republicans both have something at stake, but it could also signal a broader shift in how America prioritizes defense spending in a time of scarce resources. President Barack Obama's decision in July to begin withdrawing troops from Afghanistan captured this sentiment in responding to a chorus of Congressional voices pointing to the soaring cost of the war. With the American economy still sputtering and Afghanistan consuming a huge amount of taxpayer money, it was time, Obama said, to focus on "nation building at home." Obama has also sought a reduction of about $400 billion in defense spending by 2023.

Congressmen allied with the Tea Party proved themselves to be formidable in the debt talks, helping to undercut any compromise that didn't cut deeply enough or that included new revenue. But while this position made them natural antagonists of Obama, they could prove to be an ally if he continues pushing to curtail defense spending. Many of the newly elected Tea Party lawmakers espouse a vision of a limited U.S. military presence that is consistent with their goal of shrinking government. Sen. Mike Lee, R-Utah, and Sen. Rand Paul, R-Ky., have been particularly vocal on that front.

There has been some pushback. Sen. John McCain has repeatedly warned against "misguided and excessive reductions in defense spending," Sen. Joe Lieberman voiced his concern that the deal would "disproportionately cut defense spending and result in unacceptably high risk to our national security " and The Washington Post reported that defense hawks constitute a main source of opposition to the deal.

But McCain has said he will "swallow hard" and accept the deal, and the looming risk of default will likely provide the leverage to convince others to do the same. In a new era of austerity, the military's budget -- and by extension, America's unrivaled military capability -- may no longer be sacrosanct.