If a pro-European candidate doesn't win there, the European project may instead be forced into a long, cold winter, and nationalist, protectionist and populist agendas may once again take the upper hand.

The French presidential elections, run in two rounds on April 23 and May 7.

Le Pen is very likely to advance to the second-round final vote with Emmanuel Macron, the leading centrist candidate. Both politicians poll at about 25% currently, well ahead of other contenders. In the second round, Le Pen is expected receive only around 35% of the votes. That is well below the poll numbers of 2016's seminal election winners: the "Leave" campaign in the U.K., and Donald Trump in the U.S. elections. But a terror attack or political bombshell might still make Le Pen a real contender in that final round on May 7.

The reasons for that are multifold, but the fact that France was the European focal point for terror attacks in recent years, and has for years had a complicated relation to immigrants, certainly plays a major role.