is my baseboard heating unit malfunctioning
If the pipe is very hot going in and out of the baseboard then its probably not a problem with the boiler.  You can try turning the water temperature up on the boiler. They normally go up to 200 but i would not go higher than 180 for efficiency.  Every boiler is a little different on how to do this.  Also if you have exposed pipes or radiators it should be lower to avoid burns

It is most likely something in that basement that changed letting in more cold air or its just  being extra cold outside.