How exactly do ordinary Americans follow astronauts to Mars in that way?
There is NO comparison.
As colonists.
I agree . . . They can't follow in that way, at least not immediately. In fact, ordinary Americans probably won't be able to follow for a long time. The technology and infrastructure have to be developed and put into place first. As Dubya said, we're doing it "in the spirit of discovery, to learn the potential of vast new territory, and to chart a way for others to follow." That's the comparison to Lewis and Clark we need to focus on, imo, and not so much on beaver pelts and the like. It'll never be like that.