Donald Trump wrote an extraordinary letter to Turkey’s President warning him "don't be a tough guy" or “a fool” as he called for an end to the military offensive in Syria.
The US leader said Recep Tayyip Erdogan risked being remembered as the "the devil”.
Mr Trump's strongly-worded letter was made public on Wednesday night but dated two days after US troops were ordered to pull out of northern Syria.
He wrote: "It will look upon you forever as the devil if good things don't happen. Don't be a tough guy. Don't be a fool!"
The US President started the October 9 letter by suggesting that the two leaders could "work out a good deal."
But he told Mr Erdogan he did not want to be responsible for "slaughtering thousands of people."
Mr Trump said he did not want to impose sanctions that would cripple Turkey's economy if Ankara invaded Syria to battle Kurdish forces.
The letter emerged after Democrats claimed Mr Trump had a "meltdown" during a meeting with Congress earlier.
The meeting followed a vote in Congress rebuking the US president's decision to pull forces out of Syria that was backed by an overwhelming majority of Republicans and Democrats.
Both sides of the House came together and passed a non-binding resolution by 354-60 votes.
House Speaker Nancy Pelosi said the meeting was cut short after Mr Trump had a "meltdown" over a House of Representatives vote condemning his Syria withdrawal.
"I think that vote - the size of the vote, more than 2-1 of the Republicans voted to oppose what the president did - probably got to the president. Because he was shaken up by it," Ms Pelosi told reporters.
"And that's why we couldn't continue in the meeting because he was just not relating to the reality of it."
"What we witnessed on the part of the president was a meltdown. Sad to say," she told reporters as she and the other Democrats emerged from the White House.
The Democratic leader said Mr Trump had a temper tantrum because of the number of Republicans who joined Democrats to vote for a resolution condemning his decision to withdraw US forces from northeastern Syria.
The move cleared the way for Turkey's offensive against US-allied Syrian Kurds.
