The US is surrounded by 2 oceans and friendly countries as far as one can see (well, barring Cuba, but blockading Cuba could not be easier, and making them an ally would be even easier).

The US is unlikely to be engaging in fighting on its own territory and any ground fighting will likely be in Asia.

It’s very hard to see a situation where it’s logistically feasible for the US to transport so many people over that it exceeds the number of soldiers already in the military.

It’s likely thst if a war is going badly enough to conscript people, the US would decide to stop fighting it continents over well before it gets to the stage of a draft.

Especially in modern warfare where it’s becoming extremely Evident that unmanned drones will play the bulk of the role of actual fighting.