If ever a speech seemed to be President Obama's last, best chance to win public and congressional support for his plan to launch military strikes against Syria, it's his prime-time talk to the nation Tuesday.

With polls indicating that 60 percent of Americans oppose action against Syria for using sarin gas and congressional approval looking ever more like a long shot, Obama's speech is a high-stakes endeavor.

What can viewers expect to hear in the speech? It's likely they've already heard most of the complicated case that Obama and other administration officials have made in recent weeks — though there's the new twist of a Russian proposal that Syria put its chemical weapons under international supervision.

That latest turn of events is already rippling through the U.S. debate.

Still, the White House has indicated every intention to seek congressional approval for military action. White House Deputy National Security adviser Tony Blinken essentially laid out the main points at a briefing Monday.

They boil down to these 10 words or phrases: congressional authorization, intel, violated international norms, U.S. laws, national interest, U.S. credibility, a political solution, the new Russian initiative, limited military action and the risks of inaction.

That's an undeniably long list of reasons for a U.S. attack on Syria, causing at least one writer to accuse the administration of the equivalent of throwing spaghetti on the wall to see what sticks.

Anyway, let's move through the points the president will likely make in Tuesday's big speech, lumping some of the related ones together in order to move through them more quickly.

Congressional authorization, U.S. credibility, U.S. laws and national interest — Obama will likely note that he sought to do the right thing by seeking congressional approval before any attack and that lawmakers should do the same, at least in his eyes, by granting approval.

With the decision to put the question before Congress, "it's important that he emphasize to both Republicans and Democrats that the country's prestige is on the line and that failing to deal with Syria would not only have enormous ramifications for our dealings with North Korea but Iran as well," says Jim Manley, former press secretary to Senate Majority Leader Harry Reid, now with the Quinn Gillespie lobbying and communications firm.

The administration notes that Congress passed the Syria Accountability Act in 2003 partly as a response to Assad's stockpiling of chemical weapons.

By crossing Obama's "red line" against using them, Assad has now lowered the threshold for their use again, threatening regional U.S. allies like Turkey and Israel, and neighboring Lebanon, which runs counter to U.S. interests.

Intel and violated international norms -- Expect Obama to once again assert that intelligence is conclusive that the Syrian military used poison gas against civilians. It's a level of reassurance necessitated by the nation's experience of having invaded Iraq on the basis of bad intel.

Tom Perriello, a former Democratic congressman from Virginia who opposed the Iraq War but supports the proposed U.S. action against Syria, said the lawmakers he's talked to are persuaded.

"The things I've heard fairly consistently are, people walk away convinced that the Assad regime committed these atrocities and that there are targets we could hit that would inflict meaningful strategic pain on the Assad regime without significant collateral damage," said Perriello, president and CEO of the Center for American Progress Action Fund.

Thus, strong intel indicates Syria violated international norms — requiring a response. Obama will likely push this line hard.

"First, I think he's got to explain why nearly a century ago the United States led the effort to make chemical weapons usage illegal because of the threat we believed it presented to our troops and to innocent civilians across the world," said Perriello. "Second, I think he has to explain why there's a value to us of deterring the use of chemical weapons even if it doesn't solve the larger conflict. If you have cancer and you get shot in the leg you're going to want medical attention to address the leg wound even as you continue to fight the cancer."

Limited military action — Obama is a president who mostly appears to share the public's war weariness. That's why he will emphasize that military action against Syria isn't like invading Iraq or Afghanistan.

"He will, of course, be emphasizing that the duration will be limited and he'll be emphasizing that targeting will also be limited," said Jim Leach, a former Republican congressman from Iowa who now teaches at the University of Iowa Law School.

While the president will likely make the point that it isn't his intention to involve the U.S. in another country's civil war, he has a knotty problem that his speech is unlikely to disentangle, Leach suggests.

"The obvious dilemma is once you intervene in a civil war you take sides," said Leach, who for years was a senior Republican on the House International Relations Committee. "And so, is that something we should be doing? And if we should be doing it, how should we be doing it? And so he has a terrific challenge. I think it's going to be a very tough sell. That doesn't mean it can't occur."

A political solution, the Russian initiative and the risks of inaction -- Expect Obama to repeat the administration's position that no military solution exists and that Assad and his regime's opponents will need to reach a political answer.

Meanwhile, the Russians, Syria's long-time allies, added a new wrinkle to the situation when they seized on comments by Secretary of State John Kerry that U.S. military action could be avoided if Syrians placed their chemical weapons under international supervision.

In network interviews Monday, Obama held out the possibility that a way forward without U.S. strikes might be possible if the Russian proposal proved real.

That's a big "if" for some.

"The problem is nobody takes Russia seriously on this," said Perriello. "If Russia's willing to back up its word with any indication of something real, I think that would a positive thing. But I'm not holding my breath."

Obama is likely to acknowledge concerns that there are risks, but also to argue that the risks of inaction outweigh the risks of action.

The problem is that so many of those who agree with Obama that Syria's behavior was abhorrent aren't willing to take the leap to military action.

"We all have strong feelings and I certainly have strong ones," Leach said. "I would recommend caution."

Still, "it's really key that this be the type of speech that we can all respect, even though many people will differ," Leach said.

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