"A US official says as commander in chief, the president has power under Article II of the Constitution to use force overseas to defend US national interest," reports CBS News.

"The official said that the US has a strong national interest in promoting regional stability, which the use of chemical weapons threatens. The official added that this justification is similar to what President Obama used in 2011 to use force in Libya. The White House also argues that the chemical weapons use violates a 2013 deal for Syria to get rid of them."

That's from this very useful Q&A from CBS News explaining how Trump was able to strikes without the approval of Congress.

Foreign Relations Committee Chair Bob Corker, a Republican, did not insist on Congressional approval prior to the strikes. However not all Republicans are convinced Trump's decision to go it alone should be repeated: