They were at best marginalized if not outright ridiculed until the financial crisis hit. Once they realized a whole lot of people were desperate and looking for someone to hate, someone to blame for their misfortunes they also figured out this was a prime opportunity for them to rise in actual power. They reshaped their speeches, packaged their image a little better to appeal to senior citizens and angry young men then pointed a finger to immigrants, Jews, you name it - while of course suddenly featuring a deep faith in all things Christian. Complete with hatred and barely restrained racism, because of course that's what Christianity is all about.
The worst part of this? They have an excellent chance in being a kingmaker in the next elections. It will come down between the current conservative government and a leftist coalition of political powers in Greece, but it's quite likely neither will have the majority on their own. And the Golden Dawn is squarely third in the polls right now... and of course they'll be able to make a deal so that a government can be formed at all.
Neonazis in power. It's a nightmare.