Merkel is locked in a standoff with her interior minister, Horst Seehofer, over his demand for some asylum-seekers to be turned back at the border.
European stocks, and particularly the German market, have been hit once again over recent days by the possibility of political turmoil in Germany caused by disagreements within the ruling coalition over the country's migrant policy. Under fire over the inhumane treatment of immigrant children at the U.S. border, Trump is telling his supporters that an overly harsh treatment of illegal immigrants is surely better than the chaos Angela Merkel's open-door policy has created.
German Chancellor Angela Merkel says she will hold talks with other European countries on migration issues and report back to her party on July 1.
Seehofer wants Germany to have the right to reject migrants who have already registered in another European Union state but Merkel opposes any unilateral move by him that would reverse her 2015 open-door policy and undermine her authority.
Laura Bush, married to the last Republican president before Trump, took the highly unusual step of publishing a Father's Day op-ed in the Washington Post on Sunday, in which she said "this zero-tolerance policy is cruel".
If Seehofer were to defy her and go ahead with his plans on Monday, Merkel would nearly certainly be forced to fire him.
After the tweet, the president defended his stance during a press conference and repeated his claims.
The move sparked a clash between France and Italy as immigration also triggered a domestic crisis for Merkel, a leader already weakened by her decision in 2015 to keep open German borders to a mass influx of more than one million refugees.
As outlined in his "migration master plan", Seehofer wants to refuse asylum access to German territory if they have already formally entered the Schengen zone via another country.
Italian Interior Minister Matteo Salvini, who this month refused entry for a boat with 600 refugees, on Saturday said on his Facebook page the country won't permit two ships allegedly carrying migrants and asylum seekers from Libya to reach its shores. As she so often does with the men who challenge her, Merkel gave him just enough rope to hang himself.
He said all 28 European Union member states had to be involved.
By contrast, Merkel has warned of a resulting domino effect as Germany's neighbors rush to shutter their internal Schengen borders and is calling for a joint European solution to the "refugee crisis" to be reached within the next two weeks.
In an extraordinary move, the CSU - facing a tough regional election in October - has threatened to defy her and on Monday go ahead with plans for Germany to send back migrants already registered in other European Union states.
They pointed out that Germany's crime rate is at its lowest since 1992, according to Interior Ministry figures released last month.