The offer by Italy's populist 5-Star Movement to share its web platform with France's "yellow vest" protesters could be a harbinger of what's to come in the upcoming European Parliament elections.

The French movement has brought together left and right extremes within France, and Italy's government did the same with two ruling populist parties. Many on both sides see the possibility of the same tactical alliances among populist groups across the continent.

The European Parliament elections are a four-day series of national votes to be held across Europe in May that decide the makeup of the legislature. The parliament makes Europe-wide law, decides international agreements, and — crucially — can censure EU countries for violating core values.

Populist Euro-skeptics are poised to win an unprecedented one-third of the seats, under current projections by the pro-EU European Council on Foreign Relations.