evidence: While it hasn’t been invoked in over half a century, it’s mandatory for all male U.S. citizens to register for the selective service, also known as the military draft, when they turn 18. Failure to register is classified as a felony and comes with a host of legal challenges. [...] According to the Selective Service, if a draft were held today, those who are 20 years old -- or turning 20 during the year in which the numbers are drawn -- would be the first to go. Beginning Jan. 1 of the year an eligible male turns 21, he would drop into the second priority category, and men born the following year would move into the priority group one. Each succeeding year, a draft eligible man drops into the next lower priority group until he has reached his 26th birthday, at which time he is over the age of liability for the draft. [...] First, the president and Congress would need to authorize the draft. Then, Selective Service activates and orders all personnel to report for duty. Afterward, a publicly attended, nationally televised and live-streamed lottery is conducted. You can learn more about the process here.