BERLIN — Prepare for Merkeldämmerung.

Germany’s chancellor suffered a major blow Tuesday when her center-right bloc rejected her handpicked choice to lead its parliamentary group, an affront that one German commentator described as nothing less than a “political bomb.”

The news that Volker Kauder, a close Merkel ally who has run the parliamentary group for 13 years, lost in a secret ballot to challenger Ralph Brinkhaus, his deputy, sent shockwaves through political circles in the German capital.

Most observers were convinced Kauder, with the support of Merkel and other party leaders, would easily beat Brinkhaus, who has virtually no public profile. Brinkhaus, who witnesses described as surprised by his own victory, received 125 votes to Kauder’s 112.

Before the vote, Merkel made a personal plea to the group at a meeting in the historic Reichstag building, telling members that she considers Kauder to be crucial to the stability of her coalition government. By selecting Brinkhaus against Merkel’s wishes immediately following her remarks, conservative MPs left no doubt that they are dissatisfied with the chancellor’s stewardship.

"This is a revolt against Merkel” — Thomas Oppermann, senior Social Democrat

The question now is whether conservative MPs simply wanted to send Merkel a reminder of their disquiet or if the vote represents a more fundamental shift away from her, signaling the beginning of Merkeldämmerung, the end of the Merkel era.

A visibly strained Merkel briefly addressed waiting television crews after the vote in an effort to counter that narrative.

“This is the hour of democracy, in which there is also defeat,” she said, while acknowledging “there is nothing to sugarcoat.”

Other assessments were more direct.

“This is a revolt against Merkel,” Thomas Oppermann, a senior Social Democrat whose party governs alongside the chancellor’s, said on Twitter.

In Germany’s stability-obsessed political culture such open rebellions, especially within the governing party, are rare. But conservatives in Merkel’s bloc — an alliance of two parties, the Christian Democrats and Bavaria’s Christian Social Union — have long taken issue with her handling of migration and other issues, such as the eurozone bailouts, grumbling that she has taken their party too far to the left.

Though Merkel has plenty of centrist allies within her group, commonly called the Union, internal dismay over the rise of the far-right Alternative for Germany (AfD), which many conservatives privately blame on her policies, has eroded support for the chancellor. Merkel’s broad appeal to voters outside traditional conservative circles, a factor that has been crucial in keeping the party in power, has helped her keep critics in check.

The turmoil over the botched dismissal of Germany’s domestic spy chief added to growing frustration over her leadership, however. The affair marked the second time since July that the so-called grand coalition of conservatives and Social Democrats came to the brink of collapse, largely due to infighting within Merkel’s camp that she struggled to bring under control.

The fact that Brinkhaus even decided to challenge Kauder was itself considered a small sensation, as it marked only the second time since 1973 that more than one candidate has run for the position. While the parliamentary leadership post is considered a key job within the center-right hierarchy, MPs normally leave the selection to top party officials.

Close coordination between the two spheres is especially important when the party is in power, as the Union is now. Kauder, for example, has been crucial in helping Merkel push through her agenda and whipping dissidents into line, including during the Greek crisis.

It’s going to be a collaboration built on trust" — German MP Ralph Brinkhaus

Brinkhaus, 50, announced his candidacy last month, arguing that he would bring “new impulses” and act as a bridge-builder between the different factions in the group. But after declaring his candidacy to colleagues at a party meeting, no one clapped, fueling speculation that Brinkhaus didn’t have a chance against Kauder.

Notwithstanding his decision to challenge Merkel’s man, Brinkhaus, a teetotaler from eastern Westphalia, is not known as a rebel. A longtime CDU member, Brinkhaus worked in local politics before joining the Bundestag in 2009. He was elected deputy of the parliamentary group in 2014.

A tax adviser by training, Brinkhaus made a name for himself as an expert on budgetary and finance-related issues. His rhetorical skills, in particular his ability to deliver parliamentary speeches without a manuscript, have impressed his fellow parliamentarians.

“I’m looking forward to working with Angela Merkel,” Brinkhaus said after his election. “It’s going to be a collaboration built on trust.”

Brinkhaus’ reputation as a straight-shooter not known for criticizing Merkel appears to have made him the perfect person for MPs to send a warning to the chancellor and other party leaders. Intentionally or not, they may have also set a process in motion that could accelerate Merkel’s exit from the political stage.

The Union faces two important regional elections in the coming weeks, one in Bavaria on October 14 and another in the western state of Hesse on October 28. Polls suggest the conservatives, who govern in both states, will suffer heavy losses.

If that happens, Merkel will inevitably feel further pressure. With her Christian Democrats set to hold a party congress in December, a challenge to her leadership can’t be ruled out.

Much will depend on the course of the grand coalition. Though the government has only been in power since March, Germans are increasingly unhappy with it. Amid the persistent coalition infighting, voter support has fallen to just 45 percent, according to recent polls.

The opposition has seized on the growing turmoil, with some parties even demanding Merkel face a no-confidence vote.

“This country doesn’t deserve an unstable, directionless government that only fights with itself,” Christian Lindner, leader of the liberal Free Democrats, said.