It is a 16 letter word
It starts with letter p. And it has the following meaning:-

1: Parliamentarians serve the public by working on legislation and policies that would be of benefits to their constituents.

2: parliamentarians represent the interest of their constituents in the parliament by listening to their concerns and also advocating for them.

3: Parliamentarians are supposed or expected to deliver on their campaign pledges and promises.

I think my explanations fit in the clues you provided.