When a member of Congress exercises very little independent decision making, and instead advocates for what the majority of what their constituency demands, this illustrates

Gridlock

Explanation:

In simple words, Gridlock, also known as deadlock or parliamentary stalemate in politics, is a state in which it is impossible to pass legislation that meet the interests of the public. Whenever the ratio of bills enacted to the legislature's platform falls, the nation becomes gridlocked.

Laws can be thought of as availability, while legislative agendas can be thought of as demand. Where two legislative bodies, or the administrative branches and the judiciary, are governed by separate political groups gridlock will result.