Discontinue the Space Launch System (SLS) in favor of investing in private sector launch capabilities.

The Space Launch System is a very expensive way to launch deep space missions. It's approach is rooted in the 50's/60's super-heavy lift approach.
In the past 50 years we've developed techniques for earth-orbit rendezvous, allowing us to launch payloads on multiple rockets and assembling the mission in space.
The model of using a single super-heavy lift is expensive and a single launch failure would set the program back by years!
The use of multiple launches of commercial rockets is cheaper and does not put all the eggs in a single basket.
The SLS is an outdated concept. A boondoggle.