ANGELA MERKEL looks secure as Germany’s chancellor. But a battle over immigration policy in Berlin today provided a stark reminder of her political mortality—and a glimpse of the culture wars roiling her political alliance.

Germany’s centre-right is a strange beast. It is made up of two parties that sit in the same group in the Bundestag and present the same candidate for the chancellery at federal elections. One, the Christian Democrat Union (CDU), runs candidates in 15 of the country’s 16 states. The other, the Christian Social Union (CSU) is a little more socially conservative and economically statist, and runs candidates only in Bavaria; Germany’s second-largest state by population and most distinctive by culture. Together they make up one half of Germany’s so-called “grand coalition”, the other being the centre-left Social Democrats (SPD).

Today the relationship between the two is at breaking point. The CSU has long criticised Mrs Merkel’s liberal immigration policies, not least as Bavaria (with its border to Austria) was at the forefront of the refugee crisis in 2015. In October it faces an election in its home state, where it is traditionally hegemonic. Polls suggest it might lose its majority in the Munich parliament for only the second time in about half a century, thanks to the rise of the far-right, anti-immigrant Alternative for Germany party. In response the CSU is tacking rightwards.

On Tuesday Horst Seehofer, the CSU federal interior minister, cancelled the announcement of his “masterplan” for immigration. The reason: Mrs Merkel was blocking his proposal to turn back at German borders those migrants that are registered in other EU states. Under the union’s Dublin regulation the country where an immigrant arrives is responsible for his or her asylum application. But during the refugee crisis and its aftermath many have left the country where the arrived (Italy, say) to travel to another (Germany, say), where they believe prospects are better.

The chancellor fears that by unilaterally defying the Schengen system of open borders, Germany would risk a wave of similar unilateral moves from other EU states; starting with Austria, which would convey those rejected by Germany back to its own southern border. And that at a time when north-south and east-west divisions already divide the union to an extent that keeps policy-makers in Berlin up at night. Hence her resistance to Mr Seehofer’s proposal. Yet even an emergency summit last night, at which the chancellor proposed bilateral deals with countries particularly affected by the migration crisis (Italy and Greece, for example) enabling Germany to turn back certain migrants, saw her meet with resistance from the Bavarians.

The severity of the failure of last night’s meeting became clear this morning when a plenary sitting of the Bundestag was suspended so the CDU and CSU MPs could meet. Notably, in a rare departure from parliamentary practice, they did so separately. As journalists waited outside, the CDU group heard Mrs Merkel ask for another two weeks to secure her preferred solution: some European arrangement—to be agreed at the EU summit in Brussels at the end of this month—presumably providing support for those states in the union where migrants most often arrive in return for better policing of the movement of those migrants across internal EU borders. The chancellor received a positive reception and was said afterwards to have felt strengthened by the support.

Meanwhile the CSU group debated how far to push the chancellor and concluded: all the way. After the meeting MPs briefed that Mrs Merkel had little hope of securing a credible solution, that voters have no patience left with the German political class and want action now, and that Mr Seehofer should, as interior minister, order migrants to be turned back even against the chancellor’s will—an astonishing challenge to her authority. Some of the language used by the CSU MPs in the Bundestag’s lobbies today came close to justifying a vote of confidence in the chancellor, prompting angry exchanges with Merkel loyalists in the CDU. The Bavarians will confirm on Monday whether Mr Seehofer should indeed defy Mrs Merkel in this way; then the two parliamentary groups meet again on Tuesday. Sparks are sure to fly when they do.

This could end any number of ways. It is possible, but not likely, that Mr Seehofer’s challenge to the chancellor will unravel her authority, forcing her out. Even if this does not happen, a formal split between the two sides of the CDU/CSU group in the Bundestag was suggested by some irate CSUers earlier. The language used by both makes the possibilities for compromise or nuance hard to spot.

Yet to predict Merkeldämmering would be premature. The chancellor remains Germany’s most popular politician. She still commands the support of her party and most major figures in it—with exceptions like Jens Spahn, the ambitious health minister who tried and failed to marshal dissent against the chancellor in the meeting of CDU MPs. The CSU’s brinksmanship has not (yet) tipped into an all-out attempt to oust Mrs Merkel. Most likely is that she will, as is her wont, ride out the theatrics of the overwrought male politicians around her then propose some fudge and prevail; probably involving whipping out the federal cheque book at the upcoming EU summit. Do not count out the great survivor of German politics just yet.