Crew Dragon is great and Starliner might be someday as well but I dont think thats enough redundancy for national security reasons or for general crewed access to orbit.
Starliner can only launch 7 or eight times, due to the Atlas V, the rocket it’s been mated to, having already been EOL’d. Those launches have already been scheduled. So even with Starliner there is zero redundancy if Dragon hits a snag.
Source?
It isn’t trivial re-engineering and re-certifying Starliner for SLS. (Also, Starliner is designed to go to LEO. It’s a shuttle, not a spaceship. Isn’t SLS too powerful and expensive?)