It WON’T happen.
Not enough Martian voters.
(i.e. There is no constituency for that level of expenditure)
The expenditure wouldn’t be that great. NASA’s budget is tiny compared to others, and the lethargy of the manned space program has disillusioned us into thinking it can’t be done. You’ve hit on something: the public will just isn’t there anymore. It’s too bad, because we are a nation built by explorers—not afraid to go into the wild frontier and expand our horizons. Is the safety of never venturing beyond our comfort zones better?