Does the government know what it wants?

From NASAwatch:

"How do we motivate students to study astrobiology if this science is not favored in the budget?" asked a teacher. "If they want to work for government money, they must look at what the government wants - not what they think it should want. If they want to work with something the government doesn't want, they'll have to find other money to fund it," Griffin stated."

Fair enough.
But, how do you motivate students to study astrobiology, or any particular subfield, if the government changes its mind about what it wants on a shorter time scale than it takes to graduate students, much less the time scale for a student to establish a career.
That is the problem.