The chairman of the House Armed Services Committee said late Friday that it's unlikely the White House is "even contemplating" seeking congressional approval for a military strike on Syria.
If Obama decides unilaterally to engage, that would put the president at odds with more than 100 lawmakers who have signed a letter saying it would be unconstitutional for him to do so without getting authorization from Congress.
McKeon added that he's had three phone conversations with the administration and they've made it clear Obama has not yet made up his mind on how to proceed in Syria.
But he urged the president to "go to the American people and the Congress and convince them that we do know" that Syrian President Bashar al-Assad is using chemical weapons against his own people before launching military action in the nation.
On Friday, U.S. intelligence officials released a declassified report on the details of the chemical attacks earlier this month, in an attempt to bolster support for possible military operations in the country.
Shortly after the release of the report, intelligence officials headed to Capitol Hill to brief lawmakers and their staffs on classified portions of the administration's case for intervention in Syria.
McKeon cautioned that with a week of speculation over possible engagement in Syria, the U.S. may have already given the regime "too much advance warning."
"I think we've already given them too much advance warning to what we're going to do, but I think he has to lay out the case that we have sufficient evidence to show that they did this. And that we have legal authority and moral authority to respond," he said.