Jean-Marie Le Pen, the founder of France’s main far-right party, has died at 96. Anti-immigration and nationalist ideas that propelled his decades of popularity remain ascendant in the country, across Europe and beyond.

For years, the far-right National Rally tried to distance itself from Mr. Le Pen’s racist and antisemitic remarks. But after his death Tuesday, it hailed him as a visionary.

The death of Jean-Marie Le Pen, former leader of the party once known as the National Front, occurs at a time when the mainstreaming of far-right politics