Well, I'm sure that it would cause some issues at first, but I'm fairly certain that they'd be able to solve those issues. Remember when they started letting black soldiers and white soldiers serve in the same unit? There was an outcry from the conservatives who thought that it would be the end of the US army. Not so.
Women have fought in wars in the past. During the German invasion of Russia during WWII, many, many, many, many, many thousands upon thousands of women fought on the front line, in tanks, in trenches, in planes, using artillery, etc. You know that iconic photo showing soviet soldiers hoisting the red flag over the Reichstag? One of the soldiers in that photo is a woman.
It is true that the bulk of women have less physical strength than men, but we're not fighting with lances anymore. The US army is a highly technological army which depends more on technology than physical prowess. The strength of the US army isn't in the individual fighting soldier (although they are important), but in the quality of their weapons, the efficiency of their logistics, the speed of their fighter aircraft and the energy of their explosives. Women can shoot guns, pilot planes and drive tanks.
Let them serve. They'll surprise you.