The two leaders showed little common ground Friday over a host of thorny issues, including NATO and defense spending.
Today, Trump tweeted: "Germany owes vast sums of money to NATO & the United States must be paid more for the powerful, and very expensive, defense it provides to Germany!"
During their joint news conference yesterday, Trump -- who has criticized NATO as "obsolete" -- demanded that America's allies in the military alliance pay back "vast sums of money from past years."
Trump set the tone for his relations with Merkel during his campaign last year, saying her decision to allow refugees into Germany was a "catastrophic mistake" and suggested she was "ruining Germany."
He also lashed out at the news media on Saturday. "Despite what you have heard from the FAKE NEWS," he tweeted, "I had a GREAT meeting with German Chancellor Angela Merkel.