You know what...I'm not so sure of this anymore to be honest. This whole evening I've been reading on twitter and FB people saying they don't want to vote for "the banks" ( = Macron) so they won't vote on the second round. Even level-headed people, blogs, etc. While on the right I'd be shocked if a large portion of Fillon's voters didn't vote for Le Pen.
Strangely enough, Le Pen's strategy of showcasing the Front National as a "normal" party even works with its opponents : even they seem to not see the urgency to vote against her. Right now I'm quite worried that a lot of people won't vote for Macron. I sincerely hope I'm wrong though.
TLDR : It's impossible that Le Pen wins this.
I really don't get why people are so scared of this second round to be honest. It was the same in 2002 and even if JM Le Pen had way less legitimacy, the result was obvious. As you accurately stated low participation is the only reason the FN can rise (not necessarily win), a high number is always detrimental to them because they supporters are faithful but are limited in number. So to sway their percentage, they indeed need a low number of total votes so they can raise their stock relatively speaking. In 2002 when FN managed to get in the second round, the participation was at 71% and rose 9 points in the second round. 80% is usually where we max out in the 2nd round since 1995 (except in 2007 because of fresh heads, we topped at 83). Before 1995, numbers in the 2nd were even higher.
It's possible that some won't vote for Macron for legit reasons. Myself I already stated that I don't like him though he did say some interesting things in the campaign but that's all. That said, mechanically, Le Pen just can't get half the votes :
- First, she didn't win the 1st round which I thought she could but she peaked way too early and lost momentum. People voted at 77% in the first round, which is relatively high and usually this number rises in the second round but it's not a given. At 80% participants, 50% is 18M votes. Macron already did 24% and Le Pen 21% which is respectively 8.5M and 7.5M so a head start for Macron of 1M people. At 80% participants, he then needs to convince less people than Le Pen.
- Second, even if some people think that the political spectrum is a circle and that there are connexions between the far left and the far right. In practice, the ends are opposite most of the times. Therefore, on average for a far left voter, Macron will still be closer than a Le Pen and that will be true for any voter than is from far left to moderate right (considering that even Fillon which is classified in very conservative, neo liberal breh called to vote for Macron, but for the sake of the argument, let's say this type may flock to Le Pen). which is the majority. So Macron starts with a bigger reservoir of first-hand votes than Le Pen and also has a bigger reservoir of second-hand votes (even if they will peg their noses to vote for him).
- Third, historically, FN is "taboo". Even if MLP managed to successfully smoothen its image in 2017, she still slips from time to time. Even if the current gen never experienced the hard image of his father and the likes of Gollnish or Mégret which were despicable, they still have the "feeling" that FN is far from being a good thing to vote for. That's the reason why historically, the "Front Républicain" is symbolically called when FN is at the second round of an election. It has weakened since the late 2000s but it's still something that the majority of losers of the first rounds of any elections accept to call for their supporters to do. Which means that even those that vote right may chose to vote for Macron just because their dignity can't accept to be the culprits that elected FN as leader of the Nation.
All that makes it impossible for Le Pen, not only to get 18M votes but to garner more second-hand votes from Macron (whom she's already trailing behind). I would have understood (a little) the worries if the roles were reversed and Le Pen was at 24 and Macron at 21. But in the current configuration I just don't understand why people are scared. It's not over confidence from my end because we're never safe from fukkery but it's impossible for her to get 10.5M votes more than what she managed to do in the first.
Realistically, she may get around 14M votes which is huge honestly (but not guaranteed). With this number of votes, she'll need the super low number of 28M voters to win which would make the participation level at... 62% ! Which would be new record low... from 1969 at 6% lower from the previous mark. A 15 points drop from the 1st round would mean 7M less voters which makes no sense.