Some countries – the United States and France among them – place legal limits on their political leaders’ stay in office. Others, like Britain, have a rule of thumb that judges 10 years is as long as anyone should sensibly hold the top job. But Angela Merkel’s decision to seek a fourth term as Germany’s chancellor scorns such caution. If she wins the 2017 election and stays the full term, she will have governed Germany for 16 years, making her, alongside Helmut Kohl, the longest-serving German leader since Bismarck.

On one level, it is understandable that Mrs Merkel should stand again. She embodies stability at home and abroad. She is personally popular (a weekend poll said Germans want her to have a fourth term by 55% to 39%). She has no rival in the centre-right CDU (she needs to groom a successor). And these are uncertain times. Migration, the Trump presidency, the Russian threat, the Brexit vote and the eurozone crisis, now focusing on Italy – all threaten the stability that Germans treasure. Unsurprisingly, Mrs Merkel feels duty-driven to run again, while German voters seem to like Hilaire Belloc’s advice to “always keep a-hold of Nurse/ For fear of finding something worse”.

There are good reasons for Mrs Merkel’s decision. In uncertain times, it is reassuring that the leader of Europe’s most important nation holds to the principles of freedom, openness and democracy that have helped to rebuild and reunify postwar Germany. She got plenty wrong about the migration crisis, but her liberal approach contrasted with the anti-migrant upsurge elsewhere in Europe. Her decision to stand up to Vladimir Putin in Ukraine has checked some Russian ambitions. If Italy is forced out of the eurozone or Marine Le Pen is elected in France, Europe may be better able to ride out the challenge with her at the helm.

Yet Mrs Merkel knows how things unravel in German literature’s most famous work when Goethe’s hero Faust wishes aloud that everything could remain the same for ever. That is not possible today either. The Germany and EU that Mrs Merkel may lead at the end of this decade are very different from the Germany and EU of 2005, when the glow of European post-cold-war stability and growth still applied. They must adapt again if they are to prosper. That means forms of European cooperation – hopefully including Britain – that provide Europeans with hope and security not fear and instability. Germany cannot carry the burden of achieving this alone. Germany neither offers the security guarantee provided by the pre-Trump US, nor can it replicate America’s clout in international finance. If Mr Trump allows Mr Putin to have his way in eastern Europe and the Baltics, German coalition politics may mean Mrs Merkel will struggle to stand in Russia’s way. Yet Germany is essential to us all.

Mrs Merkel is rightly respected. But she is a hesitant politician. She said on Sunday it had taken her a long time even to decide to run again – a relatively easy decision compared with many she may face in the near future. And while many admire her, most would be hard put to define Merkelism. Asked about her big ideas on Sunday, she talked about broadband access and pensions, which are important subjects but not visionary aims. It is possible her victory would lead to realignment on the German left. But her biggest task is to hold Germany and the EU together amid rising nationalism. Italian and French voters will have large says on that, even before Germans go to the polls. So will the Turkish government, if the European parliament stops her visa-free travel deal.

It may be Mrs Merkel’s fate to stop things getting any worse, not resolve them. That is not to be sneezed at. Yet she can do better. She thinks in global terms. Since she is running again, she should make use of her practicality and trust to offer an achievable vision for Germany and Europe. This needs new thinking, not old. But Europe’s leading politician should surely lead Europe. If she doesn’t, what is the point of running again?