On what was supposed to be B-Day, Chancellor Angela Merkel took a Brexit break on Friday for a one-day trip to Assisi in Italy.

There she is presenting the city’s “Lamp of Peace” award to King Abdullah of Jordan and, on a visit to the religious order founded there by St Francis, a piece of the Berlin Wall.

Three decades after Germany’s hard border vanished, the leader who grew in its eastern shadow is deeply concerned at the prospect of a new, hard border in western Europe on April 12th.

That is the new, worst-case Brexit scenario after EU leaders gave Theresa May a fresh deadline a week ago to “indicate a way forward”. If the House of Commons in London fails to vote for or reject her Brexit deal, as EU officials fear, the way forward for the UK on in two weeks’ time is off a political cliff.

At the same moment as the UK crashes out of the EU without a deal, the inner-Irish Border would become an outer EU barrier. And the Government faces the ultimate political Catch-22 dilemma: how to simultaneously meet its EU treaty obligations to police an outer border of the bloc with its Belfast Agreement promise to respect the open Border.

Until now EU leaders have maintained a constructive silence on the issue of this political and customs border but, if no solutions are likely from London, by next week they will want answers from Dublin.

From the start, the German leader has taken an intense interest in Brexit, but - knowing that too much public interest was ripe for over-interpretation - has deferred in public to EU chief negotiator Michel Barnier.

Long before May visited Berlin after the Brexit vote, Taoiseach Enda Kenny was in Berlin to make the Irish case: Dublin was staying in the EU and expected full EU solidarity on the road ahead.

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Leo Varadkar repeated those messages at a joint press conference exactly a year ago in Berlin.

For her part Merkel described the Border question then as a “very sensitive issue of central importance” in which “Germany supports the Irish position completely”.

A day later, in the first Bundestag address of her fourth term, Ireland’s Brexit concerns was the only point she mentioned by name in a busy European political agenda. She also sent a clear signal to British officials still holding out hope that she could be relied on for shuttle diplomacy.

The German leader said she hoped for “friendly, close” relations with the UK - “but of course the relationship of the UK to the EU - given its wish to leave the single market and customs union - cannot be as close as today”.

That was music to the ears of Irish officials, hyper-sensitive to any changes of mood, colour or temperature in German remarks. Since then, they insist, things have remained consistent. The German leader has never veered from the script, understanding the need for total discipline with Dublin.

She has tolerated no Brexit solo runs from her officials, party backbenchers or even business leaders. Holding the line with Dublin is about holding Europe together - a priority for every German postwar leader.

Though that discipline has held, the German leader has been increasing pressure on Mr Varadkar in private - during phone calls and at EU leaders’ meetings in Brussels - on how he purposes to square the Brexit circle. On a trip to Japan in February she suggested a “creative” approach to Brexit could see outstanding backstop questions pushed into talks on the future EU-UK relationship.

“We have an agreement for the future relationship, and in this future relationship one can of course address the questions that now still have to be discussed, for instance the questions that have to do with the backstop,” she said.

“There are no doubt possibilities to ensure, on the one hand, the integrity of the single market . . . even when Northern Ireland’s doesn’t belong to it because it belongs to the UK, and the wish, if possible, to allow for no controls on the border between Northern Ireland and Ireland and to solve this point.”

After a crisis-filled 14 years on the EU stage, Merkel is Europe’s longest-serving leader. She has shown an astonishing capacity to swallow entire forests of EU paper-work on bailouts, banking union and more.

She loves gristly detail, and those in the know say the German leader has become an expert on the finer points of the Belfast Agreement.

What if, she wants to know from the Taoiseach, Ireland becomes a victim of the law of unintended consequences and his insistence on the backstop causes a no-deal Brexit - vaporising the backstop and forcing a hard border? She may be in her final political act, but German leader is coming to Ireland to show solidarity - and get answers.

November marks the 30th anniversary of the fall of the Berlin Wall. At the 25th anniversary in 2014, Dr Merkel said her stellar political career was proof that “nothing has to stay as it is”. Borders can fall and, she added, political “dreams can come true.” After elbowing his way to the top job in Dublin Varadkar now knows: nightmares too.