“How much is enough?” said Jacob Stokes, a defense expert at the centrist Center for a New American Security. “In an ideal world, you manage your risk down to zero, but that’s at enormous cost.”

Meanwhile, the strain of health care and pensions on the military’s budget is taking a greater toll.

“In the last 10 years, defense health care costs are up 83 percent, and personnel costs are up 40 percent,” Stokes said. “These costs are eating us alive.”

Michael O’Hanlon, a defense expert at the center-left Brookings Institution, said a leaner military could be as effective, as long as it innovates. He said the military could save billions of dollars, for example, by rotating crews on and off ships patrolling in vital zones, thereby reducing the overall number of ships needed to patrol a region.

More savings could result by cutting the fleet of the controversial – and expensive –experimental F-35 fighter jet in half, to about 1,200 planes.

“These sorts of changes could preserve the core elements of U.S. defense policy,” O’Hanlon said. “It’s not time to rethink everything. But there’s a ton of money to save.”

Johnson of RAND said that instead of focusing on more expensive new-generation technology for new weapons, why not use the best existing technologies? The F-35 is projected to cost about $130 million a jet, vs. the F-16, perhaps the world’s most successful fighter, which costs under $20 million a jet. Simply focusing on upgrades of the F-16 instead of building the new jet could save hundreds of billions.

Even as the United States focuses on maintaining military might, Johnson said building up the strengths of allies and partners to help deal with traditional problems should be an element of a long-term security.

“We’re really good at high-end, intel-intensive warfare,” Johnson said. “We struggle at response to instability.”