Quotes from the links, 

"…authority over the actual composition of the military belongs to lawmakers thanks to the stipulation in Article I, Section 8 that Congress has the power to “raise and support armies …. provide and maintain a navy …[and] make rules for the government and regulation of the land and naval forces.” 

Just as the president must seek congressional approval for declaring war and appointing inferior officers, so must lawmakers eventually approve changes to the armed forces."

"The two-month waiting period is called for in the legislation passed late last year that ended “don’t ask, don’t tell,” the 17-year-old law that banned openly gay men, lesbians and bisexuals from military service."