He also confused Syria with Iraq.
Trump said the U.S. “could have gone bigger” in terms of its military response but “thought this would be the appropriate first shot.”
The U.S. Secretary of State faces a tough negotiation in his Moscow visit after accusations of Russian complicity in Syrian chemical attacks.
Turkey, Saudi Arabia, the United Arab Emirates, Jordan and Qatar are to present a united front against Assad.
Most Americans approved of the president's decision to strike a Syrian air base but are not convinced he should take further military action.
Sadr, who has a huge following in Baghdad, is the first Shiite leader to call for Assad to give up power in Damascus.
Putin’s penchant for military aggression abroad to shore up his popularity at home may need a rethink.
McMaster said the missile strike against Syria was to meant to send a "strong political message to Assad," saying the White House was “prepared to do more."
The militant group launched a suicide vehicle attack on the southern Syrian base on Saturday.
Militants attacked a base with an explosive-laden vehicle and also targeted a convoy of rebel fighters.
Moscow had its S-400 missile system in range of the strike.
Syria's war, now in its seventh year, has killed hundreds of thousands and drawn local and international forces into a deadly contest for power.
Russian politicians have criticized the U.S. airstrike on the Syrian military.
The timing of the airstrikes may make for a day of uncomfortable meetings between the president and his Chinese counterpart.
Its payload, range and navigation benefits explained.
The president’s decision to strike a Syrian air base was in reaction to the suspected chemical attack in Khan Sheikhoun on Tuesday.
While Trump stopped short of calling on Assad to leave office, the comments were his strongest suggestion yet that the United States may be edging toward a stronger stance against Assad.
"American policy is based on creating chaos in different parts of the world and creating conflicts among states. This is not new," Syria's President Bashar al-Assad said.
Turkey's justice minister accused Bashar al-Assad of conducting a chemical weapons strike on Tuesday.
The killing took place in the al-Mayadin desert near Deir Ezzor city, according to a rights monitor.
Russia attempted to refute claims that the Assad regime was responsible for a suspected chemical attack that killed at least 72 people.