Marine Le Pen’s budget brinkmanship is a manageable risk. Longer-term institutional and political crisis is not.

Now, the gap from Germany to France stands at almost 0.9 percentage points — the widest since the wild days of the Eurozone debt crisis a decade ago, when investors rushed for the safety of Germany.

The struggle against Macron cannot be left to parliamentary maneuvers by the neo-fascist Le Pen and Jean-Luc Mélenchon, whose ...