The Space Shuttle and ISS have consumed an enormous amount of money and design and engineering talent from the US. The US, too, has asked for assistance from other countries, with varying success. As the projects wind down, the brain drain has been inevitable and the cost of wars and financial finagling has left the country on the ragged edge of bankruptcy.

There never will be another era such as Apollo, Shuttle and ISS. Mars, someday, will be a collaboration of directed economies which will be able to divert the wealth necessary, not the US or at least not the US as a major player.

Kinda like French astronomy.