Looking at the issues mentioned in the summary:
- economy: the government does not have direct control over the economy. At best, they can hope to attempt to influence economic development. Yet they cannot make promises.
- illegal immigration: the government does not have direct control over illegal immigration. At best, they can hope to attempt to deter illegal immigration through expensive or draconian policies. Again, they cannot make promises.
- terrorism: the government does not have direct control over terrorism. At best, they can make the life of terrorists harder but they cannot hope to stop terrorist activity and detecting it is extraordinarily difficult. Once again, they cannot make promises.
- space: the government does have direct control over federal agencies (e.g. NASA) and its contractors. While they cannot violate the laws of physics, they can certainly have fairly reliable results if they consult with scientists, engineers, and administrators to ascertain what is realistic. In other words, they can make promises.
Incidentally, none of this is specific to space exploration. Figuring out what you have some degree of control over should be one of the things that anyone considers when evaluating campaign promises.