If recent polling is any indication (and in Bavaria, it’s been known to be spot on), the Greens could secure as much as 18 percent of the vote on Sunday, more than doubling its result from Bavaria’s last state election, in 2013. Such an outcome would put the Greens ahead of the center-left Social Democrats (who are projected to win 11 percent of the vote, down from 20.6) and the far-right AfD (projected to win 10 percent). It would also put them second only to the CSU, which is expected to take 33 percent of the vote—a considerable drop from its nearly 48 percent finish in 2013.

Such a result would be disastrous for the ruling CSU, putting it well below the majority it needs to govern in Bavaria without a coalition partner, as it has for every term but one since 1966. Nor does it bode well for the national standing of the party, which governs alongside Merkel’s Christian Democrats, its center-right sister party, and the Social Democrats in coalition. Though the results of the regional election won’t affect the party’s presence in the Bundestag, the German Parliament, a poor result could put pressure on the party’s chairman, Interior Minister Horst Seehofer, to resign and give his party the opportunity to promote someone more popular to the role instead.

So just how did the CSU get to this point? As with many issues that have vexed German politics in recent years, it goes back to 2015. Bavaria’s efforts at the time earned the state worldwide praise, but it also sparked anti-immigrant sentiments that quickly buoyed the electoral rise of the anti-immigrant AfD in the years that followed.

This left the CSU with a choice: pursue a hard-line immigration policy to siphon off AfD voters, or risk being outflanked by the far right. Leopold Traugott, a policy analyst at the London-based think tank Open Europe, told me this quandary hemmed in the CSU. “They’re bleeding out voters to the AfD on the right, but if they want to stop that movement, they end up losing voters at the center,” he said. “It’s a difficult problem for them to square.”

Ultimately, the CSU did move to the right, marked most notably by Seehofer’s call in June for Germany to begin turning away asylum seekers at its border who have already sought asylum in another European Union country—a plan Merkel flatly rejected. Though a compromise was eventually reached the following month, the government infighting over the issue proved enough to turn some CSU supporters away from the party, even prompting some 15,000 people to turn out in protest of its leaders’ “irresponsible politics of division.”

Further reading: Why a small Jewish group is supporting a German party with anti-Semitic ties

But the CSU’s rightward shift also left a political void at the center—one the Green Party was happy to fill. Over the past year, the Greens have attracted 5,000 new supporters, surpassing 70,000 members for the first time in its history. Of the voters projected to support them on Sunday, the German pollster Forsa estimates that 25 percent of them are coming from the CSU. The largest share—42 percent—is believed to come from the Social Democrats, who are still reeling from their poor performance in the country’s general election last year.