That nerve gas attack killed roughly 1,400 people, including 400 children, White House officials say.
Polls show the public generally opposes an involvement in the complex and brutal Syrian civil war. Swing voters are especially opposed, and phone calls to legislators from politically active people are overwhelmingly against the strike.
The measure will likely pass in the Senate, but seems set to fail in the House.
A third of House legislators have announced their opposition, while only a tenth of of the legislators have announced their support. Neither Democratic nor Republican leaders are pushing their members to support the planned strike.
“I expected this. This is hard. I was under no illusions when I embarked on this path,” he insisted Friday.