Very low. Vastly lower than brexit/trump polls showed
I think Macron is also really helping with that. Nationalist rightwing parties have their big chance to rise to power when they "oppose" "the old elite", the old, established parties and politicians they can blame and use as scapegoats for everything and presenting themselves as the only chance for "change".
Yet Macron is young, a new face, charismatic, has a very different political point of view but still tolerant, pro-EU and appealing to a large part of the electorate. He offers a different, less controversial option for change. Just like Schulz in Germany he is the worst nightmare for those right wing parties as he siphons away their protest voters they need to win, while meanwhile Trump and Brexit WILL cause an increase in voter turnout that harms them as well, the lower the voter turnout the easier it is for fringe parties to have their minority voting base have more impact on the election that they should have (see Brexit and US election).
Also fuck Le Pen, I hate Nazis and I can't stand those that either deny what happened in WWII or try to shift the blame. Your country and people were complicit in the holocaust, now admit it, stand up to it, repent, clear your conscience and make sure it doesn't happen again instead of pretending to be the good ones that never did anything wrong. That's is coming from a German. Same shit Erdogan and a large part of the Turkish population is trying to pull with the Armenian genocide. Hope Le Pen keeps slinging mud against herself, the more tarnished her false image the better.