Alternative for Germany, or AfD, has established itself as a significant political force in the 13 years since its founding, but it has never been part of any state or federal government.

That's a result of what is often called a "firewall" against cooperation with the anti-immigrant, far-right party.

That firewall faces its biggest test after AfD won a landslide victory in Sunday's election in the eastern German state of Saxony-Anhalt.