President Donald Trump's national security adviser appeared to backpedal on the president's initial promise for an immediate pullout.
A former hostage said he and victims' family members oppose the possibility.
The North Carolina pastor has been detained in Turkey since 2016 on terrorism-related charges.
Trump tweeted that “We have defeated ISIS in Syria, my only reason for being there.”
The Islamic State group claimed responsibility for the morning attack.
But the senator criticized Trump's sudden tweet on Syria and his failure to discuss his plans with America's allies.
Most Senate Democrats likely to or already declared as running for president in 2020 opposed the move.
A big, bipartisan majority voiced opposition to a "precipitous" military drawdown in Syria and Afghanistan. Democratic presidential contenders sided with...
He accelerated his plan to leave by around two months after Defense Secretary Jim Mattis announced his own departure.