I have been watching the politics surrounding spaceflight/exploration for a few years now. The truth is that Space politics (like most politics) are local. The Representatives and Senators who actually
care about space care about it because it brings jobs and funds to their districts/states. This tends to mean those Representatives and Senators are invested in the status quo.
Current national civil space programs are "nice-to-have" symbols. They lend national prestige and demonstrate technical capability.
The president took the advice of the
Augustine committee and made decisions based on it. Government programs of large scope and vague requirements quickly suffer cost and schedule growth; Constellation did just that. But there are decisions made over the past 20 years that setup the US Government to be in this very position.
When the 25th anniversary (1994) of Apollo 11's landing was celebrated, I lived in Hampton Roads area and had the opportunity to go to the Hampton Roads Air and Space Museum more than once and visit the NASA Langley facilities. At the Museum, they had a full mock-up of the
HL-20. The US Government never funded it to actually be built. Fast-Forward 20 years,
Sierra Nevada has purchased the rights to the HL-20 and is working to fly it as the
Dream Chaser. If the administration at the time had pushed to develop the HL-20 and purchase a few, there would not have been any US HSF gap. (1)
In the late 1990s, NASA was working on a concept called
TransHab. It was being looked at as an alternative to the now cancelled
Habitation Module for ISS Alpha. A lack of an escape vehicle able to carry more than 3, led to a decision that neither was needed. Fast-forward 10 years and
Bigelow Aerospace is planning to build
entire stations (CSS) using this technology. The first CSS, when complete, will likely be able to comfortably have 2x the residents of ISS Alpha (12 vs 6).
In February 2001, the X-33 flight demonstrator program was cancelled due to material engineering challenges. The X-33 was to lead to development of the
Venture Star, a resuable- single-stage-to-orbit (RSSTO) launch vehicle and suitable shuttle replacement. It held the potential to revolutionize the American launch market. Two years later, Columbia disintegrates on re-entry and leads to the executive (read POTUS) decision to retire the remaining Space Shuttle fleet once international obligations relating to the ISS are fulfilled.
Most recently, the company that supports Space Shuttle operations/maintenance offered to
buy the rest of the fleet and continue to operate them! The US Government declined the offer.
I relate all the above to say that in my (granted limited) experience, US elected leaders do not actually care about the long term success of an American space program.