Question

Âthe broadest and most open gateway to participation is offered to the american people by _______.

Answer 1

The broadest and most open gateway to participation is offered to the American people by political parties.
If you want to engage in any type of political activity, you will have to become a member of one of the political parties. That is probably the only way to have any influence when it comes to politics, and to participate in the political life of America.