The countries of the former Soviet Union still possess the most dangerous arsenal outside the United States, but the chances of their firing on the United States are minuscule. Russia and China both have larger conventional armed forces than the U.S., and North Korea is not far behind, yet a shooting war with any of these states is unlikely. Terrorists and petty warlords in developing nations have far more modest resources at their disposal, but the probability of more assaults like the bombings of the World Trade Center and the U.S. Marines' barracks in Lebanon is very high. Therefore we must continue to defend ourselves against all three threats. In aerospace terms, this means ICBMs, stealth fighters, and helicopters.
Threat is in the eye of the beholder.
It defies consensus. This technique employs economy measures to close the gap between the dollars available for defense and the costs of adequately meeting the threats facing the nation. Three versions have been tried. All have precedents in the cold war. All have shortcomings.