Why is citizen participation essential to the preservation of the us political system

The US system is based on the principles of democracy, that is, the power is with the people, who choose their representatives.

If there is no citizen participation, then the representatives have no incentive to take decisions according to the will of the people, since they don't need to fear not being re-elected.

In this case, some could try to take over the power and establish a dictatorship.