A member of Congress acts as a delegate by voting according to the instructions of his electorate without regard for his own conscience. Members of Congress usually do not employ the delegate model of representation. Instead, they often vote as trustees, voting according to their own judgment.
The Stanford Encyclopedia of Philosophy defines the delegate model of representation as a process of decision-making in which a representative acts in line with the orders he receives from his constituents, even when these orders conflict with what he believes to be right. The notion that a member of Congress is a delegate of the people he represents is based on the democratic idea that the people are entitled to enact their will and are capable of governing themselves. James Madison, the Father of the Constitution, was a proponent of the delegate model of representation. This model is more common in international deliberative bodies than in national politics.
In actual practice, members of Congress rarely vote as delegates. Most often, they vote as trustees. A trustee is an autonomous representative who exercises his own judgment to further the national good even when it conflicts with the short-term interest of his constituents. The influential Whig parliamentarian Edmund Burke developed the trustee model of representation.