They probably will be able to do that either after the next election or after the government coalition collapses.

But as of now all they can do is b*tch and moan.

Btw, who says you can't block a party just because half the country voted for them? You can't wish the sentiment away, yes, but you can totally force them to rebuild the party infrastructure. Again and again, if needed, if they keep making an illegal extremist party.