Immigration activists, medical professionals, religious leaders, Democrats and some in Trump's own Republican Party have condemned his administration for separating almost 2,000 children from their parents at the U.S.
"This is the moment of truth for the Franco-German relationship, the hour of reckoning for the future of the euro zone", Le Maire told BMF television.
A split with the CSU, their ally of seven decades, would deprive the CDU of the governing majority it commands in the Bundestag lower house in coalition with the Social Democrats (SPD).
Merkel has had an often-tense history with Seehofer, and their relationship became really hard after Merkel's 2015 decision to keep Germany's borders open as migrants streamed across the Balkans.More news: Republicans turn on Trump's 'cruel' border policy
While Trump's assessment of Germany's crime problems is not accurate - as crime numbers in the country are the lowest since 1992, according to the most recent German data available - the brutal murder of a 14-year-old German girl has fuelled Merkel's opponents who are against the country's migration policies that provide entry to some 10,000 asylum-seekers each month. If re is no agreement, Seehofer threatens to shield German borders without chancellor's consent, which could lead to a collapse of executive in Berlin. However as I write this, on Monday evening, Seehofer has backed down. As she so often does with the men who challenge her, Merkel gave him just enough rope to hang himself.
He wants to turn away at the border new arrivals who have previously been registered in another European Union country - often their first port of call, Italy or Greece. Seehofer - then the governor of Bavaria, where most migrants first entered Germany - became a leading critic of her welcoming approach. The new populist government followed through on its election promises last week by refusing to allow a nongovernmental rescue ship to dock on its shores. But that is precisely the reason they are not going to pick up the tab if Germany tightens its border regime. Merkel opposes such unilateral action, arguing that it would increase pressure on Mediterranean countries such as Italy and Greece and weaken the entire 28-nation European Union.
Appearing before reporters in the Bavarian capital, Munich, about 20 minutes after Merkel spoke, Seehofer sounded less conciliatory, saying that once he returned to Berlin, he would begin laying the groundwork to change German policy over the chancellor's objections.
In opposing Merkel on immigration, the CSU may have a bigger aim, Mayer warns: "Arguably, their real motivation is to push Chancellor Merkel out of her office". The prime suspect is a refugee who fled back to Iraq in the wake of her disappearance. "They don't like reporting that kind of crime so they put it down as different kind of crime", he said.
Both Merkel and Macron have stressed that, as Trump openly challenges the European Union with a trade war as well as over security, immigration and climate policy, the bloc must learn to stand its ground on the world stage.