"There is a context here of rising criminality, which to a statistical degree is part of the migrant problem", he said, adding that Democrats in the US and Merkel in Germany both "neglected to their peril" the opposition among citizens to illegal immigration and lax border security.
Additionally, it was the Trump administration that chose to separate children from their families as part of its "zero tolerance" immigration policy that criminally prosecutes parents if they illegally cross the U.S. -Mexico border.
More than one million people entered Germany in the first year of the asylum policy, a majority of them coming up through Bavaria, which shares an 800km border with Austria.
Since children can not be sent to the facilities where their parents are held, they are separated from them.
And he again blamed Democrats for border security problems.
He then followed that up with an all-caps tweet that simply said, "CHANGE THE LAWS!"
"The United States will not be a migrant camp and it will not be a refugee holding facility", he said during an event on space policy.
In a follow-up tweet, Mr. Trump made the subtext of his argument clearer, which is that the US needs tough immigration laws to avoid such problems.
The people of Europe are moving farther and faster on illegal immigration than their leaders. You see what's going on there.
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".
With Berlin in the grip of crisis, Mrs Merkel is urgently trying to hold talks with other major European powers to try to broker a deal.
Meanwhile, Department of Homeland Security Secretary Kirstjen Nielsen defended the administration's immigration policies in a speech at a meeting Monday of the National Sheriffs' Association in New Orleans.
The Trump White House over the weekend released multiple, contradictory messages about its family separation policies.
None of this has stopped people from comparing Trump to Hitler. "I'll go tell him".
He went on to suggest that children were being used as pawns by "the worst criminals on earth" to enter the US illegally and then claimed he wanted to protect the USA from the crime happening in countries south of the USA border.
"We pride ourselves on acceptance", she wrote.
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.
Under the zero tolerance policy adults face criminal prosecution but their children, who aren't charged, are taken to separate facilities.
Even fervent Trump supporter and former Fox News pundit Bill O'Reilly spoke out against the tactic, calling it a "disaster for the Trump administration" in a series of tweets Monday.