The US president himself faces intensifying pressure to end migrant family separations, which are occurring as a result of a "zero tolerance" policy requiring the arrest and prosecution of anyone who crosses the border illegally.
"The people of Germany are turning against their leadership as migration is rocking the already tenuous Berlin coalition", he wrote.
Seehofer, whose party is more socially conservative than Merkel's, has always been a critic of the chancellor's immigration policies, particularly her decision to open Germany's borders at the height of the refugee crisis in 2015.
But she reiterated her opposition to Germany unilaterally closing its borders as this would pass the migrant burden on to neighboring countries, "unleashing undesired domino effects".
SORAYA SARHADDI NELSON, BYLINE: This scene three years ago of asylum-seekers thronging Munich's main train station is what the conservative Bavarian party allied with Chancellor Angela Merkel says must never be repeated.
Seehofer last week defied Merkel to announce a tough new immigration policy that would see some asylum seekers turned away at the borders of Germany.
Video shows World Cup team's plane engine burst into flames
And things went from bad to worse yesterday as they made their way to their second Group A match against Uruguay in Rostov. Petersburg to the southern city of Rostov-on-Don landed safely Monday evening and no emergency procedures were required.
A defiant Interior Minister Horst Seehofer warned that he would give Merkel a fortnight to find a European deal to curb new arrivals by a June 28-29 EU summit, failing which he vowed to order border police to turn back migrants. He called it a "big mistake" for Europe to admit large numbers of migrants. However, the European Council said it saw no point in the emergency summit due to the fact that a scheduled two-day meeting of European leaders to focus on the migrant crisis will be held in Brussels in ten days' time.
The CSU, anxious about losing votes to a new right-wing party in an October regional election, wants a ban on admitting asylum seekers into Germany who have already registered in another European Union country. Even with a sharp decline in the numbers crossing to Europe over the Mediterranean, migration has surged to the top of the political agenda, with the proliferation of unilateral measures fraying the bonds of European Union unity.
During a speech Tuesday in Washington, Trump suggested that Germany was nor being honest about its crime rate. Asked by a reporter, "if necessary, would you also support a policy which amounts to an implementation of Seehofer's plan", she replied smugly. The shocking case of a 14-year-old Jewish girl, Susanne Feldman, who was raped and murdered, has provoked alarm, even among supporters of an open immigration policy. Merkel has common sense on her side when she argues that there has to be a European fix.
Merkel and Macron agree that overburdened Mediterranean countries need financial support or incentives, and that the EU's Frontex border force must receive more funding, while Paris also advocates the creation of asylum processing centres in Africa. Merkel added, "we will no longer allow refugees who, according to the Dublin Regulation, have already been returned to the country in which they were first registered in agreement with the country in question".
Merkel said the primary goal of the budget, which could go into effect in 2021, would be to fund "investments and convergence measures".
The two leaders of Europe's biggest economies will seek to thrash out a compromise between Macron's bold vision for sweeping European Union change and Germany's stance that is more cautious, especially when it comes to finance.