After checking the battery and the starter, my first thought was a short. A couple of days ago, the starter didn't engage then, so I checked the battery connections and they were fine. Then I tried it and it started that day. It started the next few days, but it seemed like the battery was getting weaker because it took a little bit to crank. The night that it wouldn't start this time, I had actually gone to buy a jump starter as a backup in case it was the battery. So, the engine had been running less than an hour before. Jump starting it didn't work. We didn't think it was the battery itself, but we had that tested anyway.
So, to summarize:
A couple of days it ago, it wouldn't start. Starter didn't crank. Other electrical systems worked. Messed with battery cables. Started.
Ran a couple of days, but was a little slow to start.
Started that night, went to store, then wouldn't start.