Anderson talks to Sen. John McCain about the earful he's getting from constituents about possible U.S. military action in Syria.

Tonight on AC360°, Anderson talks to Sen. John McCain about the looming showdown on Capitol Hill over whether the U.S. should strike Syria for using chemical weapons two weeks ago. The Obama administration says more than 1,400 people were killed.

"This is a very, very tough call," McCain told Anderson.  Like many of his constituents, the Arizona Republican said he's also "skeptical" of the U.S. assessment on Syria because of Iraq.  However, McCain said we are "making a terrible mistake" if we allow the Assad regime to slaughter thousands of Syrians and do nothing.  "We sat by and watched and paid a very, very heavy price" during the Holocaust, said McCain. He argues we can't do the same again.

On Wednesday, the Senate Foreign Relations Committee approved a resolution allowing limited U.S. military action in Syria. However, an amendment from McCain and Democratic Sen. Christopher Coons of Delaware says any U.S. military response is intended to change Assad's battlefield momentum, stronger language than what was first given by the White House.

Does this mean McCain and the White House don't agree? And why would an attack be in the best interest of America’s national security? For those answers, watch the preview clip above and join us at 8 and 10 p.m. ET for more of Anderson's interview with Senator McCain.