In this case, it's just a measure of time. Dimorphos is in orbit around Didymos. This is why it was chosen as a target, because we can very accurately measure the difference in the length of it's orbit before and after collision.

In an inelastic collision, momentum is conserved. So Sum(momentum of all bodies) is the same before and after the collision.

If Dimorphos was a rigid body, the spacecraft would only add it's own momentum to it.

However, because the impact by the spacecraft caused just loads of material to be thrown off, the end momentum of Dimorphos is old_momentum + dart_momentum - sum(momentum of all the ejecta). Since the ejecta is going the other way, the net effect is that dimorphos was accelerated more.

(Remember, kinetic energy = ½mv^2, momentum = mv, so spreading out the energy over more, heavier objects increases efficiency.)

It doesn't matter who the Alabama senator is, or from which party. The economy of the state benefits so disproportionally from the program that anyone who gets elected will find themself in support of it.

What matters is that Shelby is one of the most influential senators, because of his seniority and connections. Whoever replaces him won't have that, and the federal spigot to Alabama is going to be turned a lot lower for a while.