SOISSONS, France — Just this spring, Marine Le Pen’s presidential campaign drew vast crowds who enthusiastically embraced her National Front’s stridently nationalist, anti-immigrant vision of France.

This week in Soissons, a somnolent provincial town far from the gaudy cast-of-thousands extravaganzas of the campaign, Ms. Le Pen was greeted by a few dozen somber National Front activists in a drab meeting hall. Even hecklers didn’t bother: Just a handful of weak-voiced protesters quickly dispersed.

Ms. Le Pen’s party, crushed by Emmanuel Macron’s 66 percent in the presidential runoff in May, fared dismally in last Sunday’s legislative elections. The National Front will most likely confirm these losses in a second round of voting this Sunday. And each day brings new revelations of internal backbiting and squabbles over strategy within the Front.

It is a head-spinning turnabout that reflects, at least for now, the fizzling of Ms. Le Pen’s fortunes in France. The National Front’s retreat also adds to the impression that far-right populism is losing its appeal more broadly.