The Libertarian Party is a centrist party within the United States, usually considered to be the main third party due to it's high national support for a third party at 10%+, they also hold a high amount of seats disproportionate for a third party.
In POWER I, the Libertarian Party were considered to be very fringe, they went through multiple leaders, all defecting to the Republican party. The longest leader they had was James Kain but under his leadership, the party dropped below 1% national support and towards the end of POWER I, it had nearly 0.3 national support.
In POWER II, they were launched very early as a party and got a head start, their leader Valladrex helped propel them to a steady position of 10% national support where they constantly waver not dropping below and rarely raising above. They have strongholds in many insignificant states such as Connecticut.