On Thursday alone, while the president was in Russia, he and senior administration officials made more than 25 individual calls to what the White House described as bipartisan members of the House and Senate. Obama called five senators himself, the White House said, but officials refused to reveal the names of the recipients.
In addition, members of the House and Senate were meeting at the White House on Friday with Vice President Joe Biden, an administration official confirmed to CNN. It was Biden's second straight day of meetings with legislators to try to convince them to authorize a military response.
Go it alone?
Should Congress reject Obama's request to authorize military strikes, Deputy National Security Adviser Tony Blinken said Friday on NPR that "the president of course has the authority" to act in Syria without support from Capitol Hill, but "it's neither his desire nor intention to use that authority absent Congress backing him."
A senior administration official from the National Security Council later clarified Blinken's remark, saying "the president's intention is to act with congressional authorization, and we believe they will vote to provide that authorization."
Asked several times at the news conference about Blinken's remark and whether he would attack Syria anyway without authorization from Congress, Obama acknowledged that he would avoid providing a direct answer.
"It would be a mistake for me to jump the gun and speculate because right now I'm working to get as much support as possible out of Congers," he said.
On Wednesday, the Senate Foreign Relations Committee approved an amended version of the White House's resolution for authorization to attack Syria by a 10-7 vote.
Senate Majority Leader Harry Reid on Friday praised the panel's Democratic and Republican leaders for working together to craft a compromise that was able win approval.
Reid spoke at a brief Senate session that allowed for the procedural step of setting up next week's consideration of the resolution by the full Senate.
Meanwhile, the House also is expected to take up the Syria issue starting Monday, with Majoriy Leader Eric Cantor of Virginia telling his Republican caucus to expect a vote on military authorization "in the next two weeks."
Approval of a resolution is considered more likely by the Democratic-led Senate than the Republican-led House.
In a step that would buy time for Obama to get more international and domestic support, Democratic Sen. Joe Manchin of West Virginia is working on a proposal that would put off any military action for 45 days while demanding that Syria sign an international convention against chemical weapons or face U.S. military repercussions, according to an aide to Manchin.
It was unclear if the idea would gain any traction among legislators considering the Syria issue.
On the sidelines of the G20 summit Friday, Obama and Russian President Vladimir Putin met for what Obama described as a "candid, constructive" conversation despite increasingly strained relations between the two leaders.
Obama acknowledged that Putin was unlikely to shift his position on military action against Syria, and Putin gave a similar account of their meeting, telling reporters that "he doesn't agree with me, I don't agree with him, but we listened to each other."
The two leaders both said they could work together to seek a political solution to the Syrian crisis, which reiterated their longstanding positions.