THE politician most thrilled by Angela Merkel’s announcement on November 20th that she will run for a fourth term as German chancellor next autumn was Frauke Petry. The leader of the populist, anti-immigrant Alternative for Germany (AfD) termed it the ultimate campaign gift: the chance to run against the very chancellor who caused the “migrant chaos”.

In fact, Mrs Merkel remains the odds-on favourite. Her support sagged during last autumn’s refugee crisis but has recovered to 55%, up from 42% in August. Recent polls suggest that the only plausible coalition against her—a left-wing combination of the Social Democrats, the Greens and the ex-communist Left party—will not win a majority (see chart). Mrs Merkel, who took office in 2005, will probably stay through 2021, overtaking Helmut Kohl to become the longest-serving German chancellor (not counting Otto von Bismarck).

Before she became chancellor, Mrs Merkel told a photographer that she wanted to make a timely exit from politics, to avoid becoming “a half-dead wreck” in office. Now she has decided she must run again. Lacking an obvious conservative successor, she may be the only one able to protect her legacy of centrist politics at a time of populist insurgencies.

The election of Donald Trump as America’s next president may have made up her mind. America’s role as guarantor of the liberal post-war order is in doubt, and some see Mrs Merkel as the last leader of stature to defend the West’s values against the likes of Russia’s president, Vladimir Putin, and Turkey’s Recep Tayyip Erdogan. As though endorsing these hopes, Barack Obama, visiting Berlin two days before Mrs Merkel’s announcement, said that if he had a vote, he would cast it for her.

The chancellor calls such perceptions “grotesque and almost absurd”. She is said to view exaggerated expectations as dangerous for her campaign. The AfD, polling at 13%, is still less popular than its counterparts in France or the Netherlands. But the mantle of defender of cosmopolitan globalism would make Mrs Merkel even more of a “lightning rod and provocation” for populists, says one insider.

So her campaign will emphasise domestic issues: security, a harder line on cultural symbols (perhaps opposing the wearing of full-face veils) and tougher rules for migrants. On the economic front, she will promise tax cuts and more investment in digitalisation. She will also exploit ambivalence in the only party that could seize the chancellery from her: the Social Democrats (SPD), who have not yet decided on a candidate. Sigmar Gabriel, the SPD’s boss, has laid down a timetable according to which the party will first agree on its programme and then sort out “personnel” in late January. He is the default candidate, but less popular than Mrs Merkel, and his announcement last week that his wife is pregnant was taken as a sign that he may not run.

Another Social Democrat, Martin Schulz, does slightly better. He is currently president of the European Parliament. But he plans to step down next year and run for the Bundestag. He might move to Berlin as early as February, to become foreign minister when Frank-Walter Steinmeier, who now runs that ministry, takes the presidency, a largely ceremonial office. From there Mr Schulz could launch his run against Mrs Merkel. Another potential candidate, Olaf Scholz, the mayor of Hamburg, is also waiting in the wings.

Among those hoping that the Social Democrats pick Mr Schulz is, of course, Mrs Petry. “Like no other German,” she says, Mr Schulz “stands for the failure of the EU.” Together, she adds, Mrs Merkel and Mr Schulz “embody the decline of Germany.” Consider the campaign launched.