For nearly 14 years as Germany’s chancellor, Angela Merkel has defined and personified Europe’s middle ground: pragmatic, consensual, mercantilist, petit-bourgeois, above all stable. It is little wonder the leader of Mitteleuropa’s major economic power has dominated the political centre for so long.

But what if Merkel falls? Can the centre hold? These are increasingly urgent questions as the once unassailable “Mutti” struggles to hold together a fractious coalition. The immediate issue, which is likely to come to a head on Monday, is a furious row over EU immigration policy. But other problems are piling up, with unpredictable consequences for Europe’s future cohesion.

Merkel’s political obituary has been written many times, but now the final draft is nearing completion. She is under fire from the hard-right, anti-immigrant Alternative für Deutschland (AfD), which stormed into the Bundestag last autumn. She has problems with the failing, unpopular Social Democrats on her left, on whom she depends for support.

More seriously, though, Merkel is being challenged from within by her interior minister, Horst Seehofer, former chairman of Bavaria’s rightwing CSU, which is allied to Merkel’s Christian Democrats. In sum, Seehofer is demanding Germany no longer admit migrants who have first entered the EU via other member states – which is nearly all of them. In Merkel’s view, such a bar would be illegal and would wreck her efforts – ongoing since the 2015 Syrian refugee crisis, when Germany accepted 1 million migrants – to create a balanced, EU-wide policy of voluntary migrant quotas. She says Seehofer should wait for this month’s EU summit to come up with a joint plan.

The problem with that approach is twofold. Seehofer’s CSU, which faces a critical electoral clash with the AfD in October, complains that the EU has been trying and failing to agree this for years. Another objection, as her critics see it, is that most Germans, recalling her 2015 “open door” policy, do not trust Merkel on this issue. Polls indicate 65% back tighter border controls.

Last week’s row between France and Italy, sparked by Rome’s decision to refuse entry to a ship, the Aquarius, carrying 629 migrants rescued off Libya, showed how improbable is the prospect of agreement at the Brussels summit. Italy’s new populist leadership, in common with an emerging axis of nationalist-minded governments in Austria, Hungary and Poland, believes it has a mandate to halt the migrant flow. Meanwhile, so-called “frontline states” such as Greece, Spain and Italy accuse “destination states” such as Germany, France and the UK of failing to accept a fair share of migrants.

Trump appears to be conducting a vendetta with Germany. Is there a misogynist tinge to his behaviour? Probably.

Divisions have been exacerbated by the failure, so far, of a key Merkel-backed initiative, the multibillion-euro EU Emergency Trust Fund for Africa, to reduce migration by addressing “root causes” in places such as Nigeria, Eritrea and Somalia. Reported scandals over the mistreatment of migrants, and inflammatory publicity given to crimes carried out by asylum seekers, stoke the tensions.

Merkel’s difficulties extend beyond one rebellious senior minister. In the view of many analysts, she has not re-established her domestic authority since the CDU lost seats in last September’s federal elections and she scrabbled for months to form a coalition. On international issues, Merkel also appears jaded and discouraged, according to close observers.

Der Spiegel paints a picture of a leader whose cherished worldview of a rules-based international order has been severely shaken by the apparent impunity enjoyed by authoritarian regimes such as Vladimir Putin’s Russia and Xi Jinping’s China. The advent of Donald Trump, the “disrupter-in-chief”, and his America First ideology has proved even more damaging than Merkel feared, Der Spiegel said.

“If Hillary Clinton had won the US election, Merkel would not have run again [in 2017],” it reported, citing a close confidant. “But that didn’t happen. In his new book about his years in the West Wing, former Barack Obama adviser Ben Rhodes writes that Merkel felt obligated to defend the free world order in the wake of Trump’s victory.”

Maybe that struggle is proving too burdensome. The immediate post-Obama days, when Merkel was hailed as western democracy’s lone saviour, are long gone, too. Trump appears to be conducting a vendetta with Germany over what he sees as unfair export practices and unequal defence spending. Is there a competitive, misogynist tinge to his behaviour? Probably.

In any event, Berlin has more to lose than most if promised retaliatory EU tariffs, which Merkel failed to water down, provoke a full-blown trade war with Washington. Meanwhile, Trump’s loud-mouthed ambassador to Germany, Richard Grenell, openly conspires with her conservative rivals.

Yet it is Europe, where the Merkel brand has been pre-eminent for so long, which may prove her biggest end-of-career disappointment. Merkel has been outflanked by the reform agenda espoused by Emmanuel Macron. France’s brash new president seeks greater European integration in financial matters, eurozone policy, development and defence. Another, separate bust-up looms over funding the EU’s first post-Brexit budget shortfall.

Many in Germany suspect Macron wants Berlin to foot the bill for his grand plan. Smaller EU states are suspicious, too. Popular pressure is for less Brussels, not more – witness the Eurosceptic mood in Italy and Greece. Rather than build a more united Europe, Macron’s ideas could tear it asunder.

Merkel’s response has been characteristically cautious. But the sense that she has lost the initiative, and is no longer the leading lady holding things together, is palpable. And, behind her back, Germany’s nationalists and populists skulk like thieves in the night, with knives drawn.