Being a bit of a conspiracy theorist I think I have an idea of what is going on here.
Look at some of the parties mentioned.
With Golden Dawn you have an ultra-nationalist neo-Nazi party to be perfectly honest. However they have spoken out against the Ukraine nationalists who they say are being used. You may have heard that America supports neo-Nazi's in Ukraine and it is somewhat true. They supported ultra-nationalists, many who share neo-Nazi views but are being used against Russia.
Front National have been doing well as of late and sent the establishment parties in panic. They are the only party who genuinely opposes mass immigration but there is more to them than that. They are critical of NATO, Western foreign policy and of course the situation in Ukraine and sanctions against Russia.
Do I think Russia is supporting these parties? I think they'd like Front National to win, but certainly not extremists like Golden Dawn.
What are the downsides?