Which aspect of U. S.politics is most closely tied to the concept of indirect democracy

political representation in both the Senate and the House of Representatives  

Explanation:

In indirect democracy, we give the people with the power to influence the government. But since it's 'indirect', we do not let the people to votes for the type of legislation directly. We select a group of people who will do it on our behalf. We called this group of people  'representatives'.

In united states, Senate and the House of Representatives  are the people who will create the laws on the  voters' behalf. The voters can freely express their opinion to them and they will vote for the legislations that will benefit their voters.