CBO Report: Illustrative Options for National Defense Under a Smaller Defense Budget [open pdf - 1MB]
"The Congressional Budget Office was asked to examine the effects on U.S. forces of a substantially smaller defense budget. Because forces can be reduced in many ways depending on the military strategy adopted, CBO [Congressional Budget Office] created three broad options to illustrate the range of strategies that the United States could pursue under a budget that would be cut gradually by a total of $1 trillion, or 14 percent, between 2022 and 2031.  Option 1 retains the 2017 national security strategy of 'deterrence by denial,' which relies heavily on U.S. combat forces to deter military aggression against allies by denying or reversing military gains in regional conflicts. The size of U.S. forces would be reduced in proportion to the smaller budget, retaining the same balance of capabilities.  Option 2 would shift emphasis from deterrence by denial to deterrence through punishment, a strategy that is similar to the United States' approach during the Cold War. The option would de-emphasize the role of U.S. combat forces in regional conflicts in favor of a heavier reliance on coalition forces in combat operations. It would call for reductions in conventional forces, such as brigade combat teams and fighter aircraft, and increases in long-range strike capabilities, such as cruise missiles, anti-ship missiles, and air defense missiles.  Option 3 focuses on maintaining the freedom of navigation in sea, air, and space around the world that the United States currently enjoys. It avoids the use of large ground forces to seize and hold territory in regional conflicts in favor of engaging enemies at standoff ranges. Although the second and third options would require the same amount of funding as the first option, they would result in different force structures and different budget allocations among the military services."
Congressional Budget Office: http://www.cbo.gov/