BERLIN — When a popular state governor was shunted aside this week, it might have been just another local political wrangle. But not in Germany, at the current moment, with the far right resurgent.

The maneuvering found Chancellor Angela Merkel’s conservatives voting with the rival Alternative for Germany, raising alarms that they had violated a taboo among mainstream parties against working with the far right. The reaction was fast and furious.

“A pact with fascism,” one headline screamed. Another gasped about “a coup.” Protesters gathered spontaneously in major cities across the country, chanting anti-fascist slogans. Even the chancellor weighed in from afar during a visit to South Africa: “It was a bad day for democracy,” she said darkly.

Three years after the Alternative for Germany became the first far-right party to enter Germany’s national parliament since World War II, the events underscored how the country’s beleaguered traditional parties are still struggling to deal with the new disruptive force.