Political parties are to express the wishes of the people.

I believe the answer is: Instruments

The role as instruments mean that political party could be used as some sort of tools that the people use to get their aspiration across the government body. This is why politicians are considered to be 'public servants', because they inherently exist to fulfil the will of the people.

i believe that the answer to the question provided above is that the role of campaign committees is to act as a bridge between state and local campaigns.