AMIENS, France — At a recent campaign rally in this economically gloomy northern city, Marine Le Pen, the gravel-voiced leader of the far-right National Front party, barely mentioned the word migrant. But, then again, she did not have to.

The supporters who turned out for her at the event here along the Somme river brought up their fear of migrants, unprompted. Ms. Le Pen’s presence alone seemed enough to evoke it.

“They are going to invade us. Then, there really will be unemployment,” said Christian Sobo, a retired building worker. “There is more help for them than for us, the French.”

His wife, Katia, chimed in, mentioning Adolf Hitler: “What he did was monstrous. But we need someone with as much force as him now.”