(ABC News) -- The White House intensified its efforts on Sunday to make the case for why limited strikes against Syria are necessary, with President Obama trying to persuade Congress and overcome a forceful tide of public opinion against launching a new military campaign in the Middle East.
The president is calling skeptical lawmakers over the weekend, aides said, delivering his pitch one-by-one to Democrats and Republicans who are either still undecided or potentially open to dropping their opposition to military strikes.
He is sharpening his argument that the United States has not only the moral responsibility to respond to the deadly chemical weapons attack in Syria, but also a critical national security imperative.
"We didn't go to Congress because we thought this was an empty exercise. We are investing a lot of time and effort in this because we think Congress should be a full partner in our national security matters. And when they are, we're stronger as a country," White House Chief of Staff Denis McDonough said on "This Week."
The heart of the administration's case to Congress and the public is illustrated in a series of videos obtained by ABC News that were viewed last week in a classified briefing to the Senate Select Committee on Intelligence.
The disturbing pictures of Syrian civilians -- many are children -- are being shown to all lawmakers before they vote on Congressional approval to the military strike.
Secretary of State John Kerry made a pointed reference to the images on Saturday in Paris, where he traveled to press the case to European allies.
"When you look at those videos of those children heaving for breath," Kerry said, "unable to move, spasming, their lives stolen from them, or their parents' lives stolen from them by gas in the middle of the night, when they should have been sleeping comfortably at home in their beds, instead they're wiped out by a man who has no conscience about what he does to his own people, are we supposed to walk away from that?"
It's a tough sell for Obama -- the toughest of his presidency -- who will make his case in a round of interviews with network television anchors on Monday, followed by an address to the American people on Tuesday.
With a vote looming in the Senate as early as Wednesday, an ABC News survey of lawmakers finds deep opposition. The administration is trying to build a coalition of 60 Democrats and Republicans to overcome the threat of a filibuster.
Vice President Biden is set to host more than a dozen Republican senators to a Sunday night dinner. ABC News has learned the guest list includes: Susan Collins of Maine, John Thune of South Dakota, Lisa Murkowski of Alaska, John McCain of Arizona, Roger Wicker of Mississippi, Saxby Chambliss of Georgia, Roy Blunt of Missouri, Kelly Ayotte of New Hampshire, Dan Coats of Indiana, Deb Fischer and Mike Johanns of Nebraska and Bob Corker of Tennessee.
A new ally for the White House is David Petraeus, the retired four-star Army general and former CIA director, who urged lawmakers on Saturday to support the military strike on Syria. Administration officials believe his support could help persuade members of Congress.
"Failure of Congress to approve the president's request would have serious ramifications not just in the Mideast but around the world," Petraeus said in a statement. "Military action against the Syrian regime is, thus, necessary not just to deter future use of chemical weapons in Syria and elsewhere, but also to ensure that Iran, North Korea and other would-be aggressors never underestimate the United States' resolve to take necessary military action when other tools prove insufficient."
In the days leading up to the Senate vote, senior Congressional aides say the challenge for the White House is not only persuading undecided members of Congress, but getting others who have already spoken out against the strike to go against the wishes of their constituents.
Dozens of lawmakers have already made their opposition known in their districts, which makes changing course a significant challenge.
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