A steady drop in water pressure from a single faucet is most likely due to a clogged aerator. The aerator is the portion on the end of the faucet spout. It mixes air with the water to provide a steady flow. It also filters out bits of debris from your main water supply and has a restrictor that helps reduce water consumption. Delta Victorian, Talbott and Pilar series faucets use a hidden aerator. Delta provides a tool for removing hidden aerators in their faucets. There is also an alternative tool if the Delta tool is not available.
Place the stopper in the sink or cover the drain with a rag. This will prevent losing any small parts down the drain in case you drop the aerator during removal.
Line up the teeth of the Delta aerator tool with the notches on the outside perimeter of the aerator. If you do not have the aerator tool, insert a quarter between two opposing notches on the aerator.
Turn the aerator counterclockwise with the aerator tool or quarter. Continue turning until the aerator is free from the Delta faucet.