The Dow Jones Industrial Average started the morning strong, rising nearly 132 points to 14933.35 before Obama met with congressional leaders on his call to punish Syria for allegedly using chemical weapons on Syrian civilians.
After the meeting, Boehner said, "I'm going to support the president's call for action, and I believe my colleagues should support the president's call for action." House Majority Leader Eric Cantor (R-Va.) also issued a statement of support. The two statements make an attack on Syria more likely.
Once the Boehner publicly said he would support the president, the Dow quickly fell more than 100 points.
At midday, the Dow was in negative territory at 14798.03.
The S&P 500 had risen 16 points to 1651.35 before the congressional meeting with Obama ended but had lost most of those gains in the aftermath.
An attack on Syria has the potential to increase turmoil in the Middle East, source of much of the world's energy supply.