BERLIN — The death threats started in 2015, when Walter Lübcke defended the refugee policy of Chancellor Angela Merkel. A regional politician for her conservative party, he would go to small towns in his district and explain that welcoming those in need was a matter of German and Christian values.

Hateful emails started pouring in. His name appeared on an online neo-Nazi hit list. His private address was published on a far-right blog. A video of him was shared hundreds of thousands of times, along with emojis of guns and gallows and sometimes explicit calls to murder him: “Shoot him now, this bastard.”

And then someone did.

On June 2, Mr. Lübcke was fatally shot in the head on his front porch, in what appears to be Germany’s first far-right political assassination since the Nazi era. The suspect — who made a detailed confession last month, only to retract it this past week under a new legal team — has a violent neo-Nazi past and police record, renewing criticism that Germany’s security apparatus, with its long track record of neglecting far-right extremism, is still failing to take the threat seriously enough.

Far-right militancy is resurgent in Germany, in ways that are new and very old, horrifying a country that prides itself on dealing honestly with its murderous past. Raw and hateful language has become increasingly common online, and politicians are increasingly under threat, with some now requiring protection.