THE term “wirkungsgleich” is hard to translate into English but means something like “equivalently effective”. It was the word of the weekend in German politics: the bar that the Christian Social Union (CSU), the conservative Bavarian sister party to Angela Merkel’s Christian Democrat Union (CDU), had said the chancellor’s European negotiations on immigration must hit to reconcile the two parties’ positions. Mrs Merkel had returned to Berlin from Brussels on Friday seemingly happy with the deals—both EU-wide and bilateral—she had forged with other EU leaders. In her summer television interview, recorded yesterday afternoon, she deemed them wirkungsgleich to the CSU’s alternative proposal: to turn back “secondary” migrants registered in other EU states at German borders. The CSU, however, begged to differ.

In a fraught eight-hour meeting on July 1st in Munich the leadership of the party (which stands candidates only in Bavaria and sits with the CDU in the Bundestag) deemed the package of measures negotiated by the chancellor non-wirkungsgleich. Horst Seehofer, Germany’s interior minister and the CSU’s leader, said that left him with three options: live with these inadequate measures, impose the new border controls against Mrs Merkel’s resolute opposition or resign. He picked the third, he told startled colleagues, who urged him to rethink. In the early hours of the morning he reformulated his resignation as an offer, with the final decision to be made in the coming days. 

MPs from the CDU and the CSU meet in Berlin this afternoon at what some fear could be a stormy encounter. Then at 5pm local time Mr Seehofer and other CSU bigwigs (including the leading hardliners Markus Söder, the Bavarian minister president, and Alexander Dobrindt, the CSU’s leader in the Bundestag) are due to meet with Mrs Merkel in a last-ditch attempt to find common ground. Both sides are stressing their readiness to compromise, but if the discussion later is unsuccessful—the chancellor reportedly told the CDU’s leadership yesterday that she could not look EU colleagues in the eye if her government unilaterally imposed the new border restrictions—Mr Seehofer may carry out his threat, resigning both as interior minister and as CSU leader.

The question then would be whether his CSU colleagues in the cabinet would join him; whether, in other words, the party would leave the government altogether. This morning Mr Söder, who would probably succeed Mr Seehofer as leader, suggested it would not: “We are completely clear about one thing: the stability of the government is not in question for us”. Erwin Huber, the CSU’s former leader, also says he does not expect the party would quit if Mr Seehofer resigned. Indeed, the latter seems to prefer to resign over acting against Mrs Merkel’s will precisely because he does not want to be held responsible for breaking up the CDU/CSU alliance, indicating that he sees resignation as the less inflammatory option. 

Nonetheless, unless one side conceded on the question of the border controls, the dispute would surely continue. Joachim Hermann, the Bavarian interior minister and a candidate to be federal interior minister if the post becomes vacant, agrees with the incumbent on the matter. Would he really back down? This morning Hans-Peter Friedrich, a top CSU parliamentarian, effectively claimed Mrs Merkel was forcing Mr Seehofer out. Amid such accusations it is not hard to imagine the resignation prompting a futher escalation of hostilities, to the point where the CSU walked out.

If so, the remainder of Mrs Merkel’s government—her own CDU and the centre-left Social Democrats (SPD)—would be just short of a majority. They could govern as a minority, but to do so would go against German political convention. More viable might be a new CDU-SPD-Green government. Robert Habeck, co-chair of the Greens, this morning declined to rule out joining such a formation. On many fronts his party might make a more natural ally to Mrs Merkel than the CSU. Whether it would choose to do so rather than embrace early elections (the Greens have risen in the polls since last September’s vote) is questionable, however. 

Amid the turmoil of a CSU walk-out, Mrs Merkel may go: either quitting of her own accord or losing a confidence vote in the Bundestag. But she would be more likely to cling on, in the short term at least. Even some Merkel-sceptics in the chancellor’s party have been horrified by the CSU’s brinksmanship, which has served to rally the CDU behind her leadership: “unilateral rejections [of immigrants] would be the wrong signal to our European partners”, read a declaration of the party’s leadership after a meeting (postponed from last night) this morning. Mrs Merkel might—might—even emerge from the current battles strengthened. 

The same cannot be said of the CSU, whose new political strategy has been far from wirkungsgleich. According to a Forsa poll published today 67% of Germans think it is acting irresponsibly; more of the party’s supporters back Mrs Merkel’s position than do Mr Seehofer’s; and its projected vote-share in Bavaria has fallen to a post-war low. If the interior minister, goaded on by Mr Söder and Mr Dobrindt, thought he could awaken a Trumpian, anti-establishment spirit in large numbers of Bavarian voters, then he misjudged them. The perception that the CSU is behaving recklessly and unreasonably (at a time when other priorities, like the escalating tariff battle with America) is becoming widespread. 

So why does the CSU persist? Perhaps the most important thing of all to know about the current dispute is that it has everything to do with emotion and almost nothing to do with substance. The number of asylum-seekers arriving in Germany every month has fallen from around 200,000 at the peak of the refugee crisis in 2015 to under 10,000 in May. Monthly arrivals of immigrants registered in other EU countries, who would fall foul of Mr Seehofer’s border regime, are in the low thousands. His plan is riddled with logistical difficulties: for one thing the Austrian government has indicated that it would not reaccept those turned back at the German border. Mrs Merkel’s European deals may be paltry, but the problem they purport to address is eminently manageable. 

Instead both sides are driven by values and pride. Mrs Merkel wants to be remembered as the chancellor who stood up for the multilateral, liberal, individual order when it was under challenge. For her to give in over the German border would undermine that central hope for her legacy. If emulated by other EU states, she rightly fears, it could end Europe’s free-travel regime.

Meanwhile the CSU is driven by antipathy towards the chancellor and her leadership style (which seems utterly to exasperate Mr Seehofer, Mr Söder and Mr Dobrindt) and blind panic about the rise of the anti-immigrant Alternative for Germany, which is eating into the party’s Bavarian support. Rather like Britain’s Brexiters, the CSU’s leaders have marched their troops up the hill and are now struggling to find a way down. Their support is dropping, the clock is ticking and Mrs Merkel is not budging. Something will have to give.