It's not really how we fight anymore. Buuuut if you want to see protests to rival the 70s, try doing a general draft again.

The US Military will never do another draft. The issue with the draft is that it instantly galvanizes opinions of every single American. Right now with a volunteer army, most Americans don't have an immediate family member that's deployed abroad. But if you institute the draft, they will.

Everyone will have a brother, husband, son, father, uncle, cousin, nephew, etc that has been drafted. And there's really nothing like a close personal connection to drive people to be upset and show it publicly. An unpopular war would become an impossible war very fast with the near-instantaneous speed of communication the internet allows. It would allow angry people to organize in very large groups very fast. The protests would be massive and unending.