FILE PHOTO: U.S. President Donald Trump declares a national emergency at the U.S.-Mexico border while speaking about border security in the Rose Garden of the White House in Washington, U.S., February 15, 2019. REUTERS/Jim Young(Reuters) – U.S. President Donald Trump said on Saturday the United States was asking European allies to “take back over 800” Islamic State fighters captured in Syria and put them on trial. “The Caliphate is ready to fall,” he said in a Tweet. “The alternative is not a good one in that we will be forced to release them…” U.S.-backed fighters in Syria are poised to capture Islamic State’s last, tiny enclave on the Euphrates, the battle commander said on Saturday, bringing its self-declared caliphate to the brink of total defeat. Writing by Nick Macfie; Editing by Sam HolmesOur Standards:The Thomson Reuters Trust Principles.