Ah the SEI... so much to say about this one... where to start ?
Bush was one of the few US presidents genuinely sincere about spaceflight (with JFK, maybe, and of course Reagan)
The timing was right at least on paper (Apollo 11 + 20 years)
...and then everything went by the drain.
As a space-mad sixteen-year-old who had been born too late to experience the thrills of Apollo, I was ecstatic.
Was seven at the time. Can't remember freakkin' SEI but same summer, Voyager flyby of Neptune was my official entry in space geekdom.
Basically the SEI stood no chance, because Shuttle and because Freedom. And because Apollo before it. the entire "logical" sequence
LEO manned flight (or Shuttle) > station > Moon
... has been thrown into chaos by JFK in '61
Moon first and then... "retreat to LEO, that sucks ! Well Mars is too far." Chaos still lasting to this very day, since we have still not return to the Moon since Apollo come too early, for the wrong reasons, and thus was cut brutally.
Basically the SEI was doomed by
- The Shuttle, already doomed since Challenger but running forward like a duck-without-a-head, until 2011
- Freedom, started in 1984 in the worst possible way, nearly canned in 1993, started for real in 1998, finished in... 2011. Dang.
Crucially, with the Shuttle a very shitty piloted vehicle, and Freedom on the wrong track from day 1 - how can you dare proposing going to the Moon or Mars ?
Both Shuttle and Freedom were completely ILL-SUITED to SEI. There was nothing to do with them in the plan, they were technically unsound, and their huge costs doomed everything else.
What would be needed to make the SEI suceed ? hard to say. Really, the Shuttle and Freedom were so bad, yet so engrained into NASA mind and planning and consciousness, it is pretty much a lost cause.
Also the 1989 SEI was a rethread of the equally bad 1969 IPP / Paine plan / Space Task Group / 1969-push-for-Mars, and the results were equally bad.
The 1969 plan was shot down by Nixon yet it remained engrained into NASA and shot down again in 1990 for the very same reasons.
That's why my TL starts from zero, not in 1989 but in 1972, strangling the Shuttle in infancy, moving Freedom forward and on a much more modest format - to kill the "space station ghost" left by Apollo, for GOOD, before (hopefully) moving back to the Moon in the 90's, and on the cheap.
Basically it is better to let the STG plan die for good in '72 and NEVER come back in the shape of the SEI 20 years later. Clean the mess in 69-72 rather than let it sleep for 20 years and come back with equally devastating results.