How definitive/likely to go through are NASA "orders" by congress/lawmakers etc.?

For a while now I've been noticing a large number of news stories saying that NASA is being "ordered" to do X, Y and Z. In two minutes of googling I found stories about a deep space habitat, a Europa mission, and just recently a mission to Alpha Centauri.

Does this mean NASA has to go through with these concepts, no matter how far fetched or overly ambitious they may be? What would be the consequences of these missions not being pushed?

Also, are all of these ideas being pushed by people well-minded to actually make these decisions? Without being too politically minded myself, I am aware of there often being a disturbing lack of connection between the opinions held in congress and the scientific community.

Thanks.

Submitted May 24, 2016 at 11:59PM by SaveOurSeaCucumbers http://ift.tt/1TyuJgY