BERLIN — The populist surge that has left Hungary, Austria and Italy threatening to close their borders to migrants has now spread to Germany, where it could even bring down Chancellor Angela Merkel and further unhinge Europe Union’s cohesion and stability.

In recent days, Ms. Merkel has faced an increasingly virulent mutiny over the issue, which threatens to fracture her governing coalition as early as next week.

The mutiny is led by her own interior minister, Horst Seehofer, a former Bavarian premier with a towering stature and plenty of beer-tent charisma, who sounds more in line with the nativist forces shaping politics in neighboring countries than with his own boss.

His region found itself on the front line of the refugee crisis in 2015, when Ms. Merkel opened the borders to hundreds of thousands of migrants who poured into Bavaria. He has long been an outspoken critic of her decision, and in recent days the two leaders have been locked in a standoff.