Third parties have shown their power by doing the following.

they have controlled the house of representatives.

they have controlled the senate.

they get the major parties to react to issues.

they have elected presidents.

Third parties have shown their power by getting the major parties to react to issues.
Since they are usually too small to impact the House of Representatives, the Senate, or elect presidents, they resort to something less impactful,such as the third option.  

Ibelieve b) recall election