"They call him a Spy, but I am more a Spy than he is", Trump wrote.
Trump called Brunson "a fine gentleman and Christian leader in the United States" who "is being persecuted for no reason".
Brunson, who's accused of espionage and assisting terror bands, needs to really be allowed to "allowed to come home to his family at which he belongs", Trump explained.
The president's tweet had drawn about 74,000 likes and 38,000 comments by Wednesday night.
Wess Mitchell, the United States' top diplomat for Europe, said the charges against Andrew Brunson, 50, of North Carolina, were "laughable". Stand with the ACLJ as we work on the worldwide front as well as at the highest levels of our government to keep Pastor Andrew's case in the headlines. Differences over strategy in Syria, as well as Brunson's "protracted detention" have damaged relations, the newspaper reported. He is accused of "Christianization", an alleged act of "terrorism" for which he could be sent to prison for 35 years.
"According to Mr. Cem Halavurt (Turkish attorney representing Pastor Brunson) Turkey has resorted to false testimony by secret witnesses, stating in the recent interrogation report that, 'This is one of those operations that we all have witnessed in many investigations within the Turkish judicial system with fake digital data and directed statements by secret witnesses".
Last May, at a face-to-face meeting with Erdogan in Washington, Trump called for Brunson's release, the White House said at the time.
In March, Tillis visited Brunson in prison. Open Doors is a non-profit organization that supports Christians in countries that face persecution for their beliefs.
USA officials have been working to release Brunson since he was arrested in 2016, following a failed coup against Turkish President Recep Tayyip Erdogan, resulting in more than 50,000 arrests.
Brunson has been imprisoned in Turkey since 2016, when Turkish officials allege he supported a failed anti-government coup.
In September past year, Erdogan suggested that Turkey could free Brunson if Washington handed over Gulen, who lives in self-imposed exile in Pennsylvania.
"We believe that Turkey is a state bound by the rule of law, and we have faith in the Turkish people's commitment to justice".
"I want the whole truth to be revealed", Brunson told the court. I love Turkey. I've been praying for Turkey for 25 years.
"I do not accept the charges mentioned in the indictment. I had no relations with anyone engaged in such activity", Brunson said. "I did not join an Islamic movement".
And the dustup comes amid tensions between the USA and Turkey over the conflict in Syria, where Turkish officials have claimed the U.S.is intentionally stalling the fight against Islamic State militants.
Also attending were the US Ambassador for Religious Freedom, Sam Brownback, and Thom Tillis, a US senator from Brunson's home state of North Carolina.
"Give him (Gulen) to us, and we will try (Brunson) and return him", Erdogan said previous year.
Gulen denies any role in the failed coup and says his Hizmet (Service) movement promotes a peaceful form of Islam.
"Everyone in the family is holding their breath", said Jacqueline Furnari, Brunson's daughter, who was raised in Turkey but moved back to the US several years ago.