WASHINGTON (CNN) -- President Barack Obama faces the challenge Tuesday night of trying to sell a military intervention he never wanted to an American public that opposes it.
The reluctant president's task has been further complicated by the sudden emergence of a possible diplomatic solution proffered by Russia that would avoid Obama's planned attack on Syria for allegedly using chemical weapons.
Under the Russian plan, which still lacks any details, Syria would turn over its chemical weapons stockpiles to international control.
That would meet Obama's main criterion of ending the chemical weapons threat by the regime of Syrian President Bashar al-Assad, which the United States says killed more than 1,400 people in a sarin gas attack in suburban Damascus on August 21.
However, Russia canceled a U.N. Security Council meeting it had called for Tuesday and rejected an initial proposal by France for the framework of a resolution, raising questions about whether the diplomatic effort that arose Monday was serious or a stall tactic to put off a U.S. attack on Syria.
New offer impacts Obama's challenge
For Obama, the new development further muddied an already difficult challenge he faced in the planned speech to the nation.
Originally intended to win over a skeptical public for another military campaign halfway around the world, the president now seeks to persuade the American people and Congress to maintain the threat of a U.S. attack on Syria while asking for time to let the diplomatic process unfold.
A White House official said Tuesday that Obama's address would cite the diplomatic opportunity at hand for his decision to temporarily put aside the option of military force.
Earlier, the president asked Senate Democrats to hold off on taking up a proposed resolution authorizing military action.
Senate Majority Leader Harry Reid then canceled a briefing on Syria for legislators planned for Wednesday, saying there were too many moving parts at the moment.
The briefing was part of the administration lobbying effort to win congressional authorization for an attack.
Still, the president and his team believe that maintaining the threat of force is necessary to pressure Russia and Syria.
"Nothing focuses the mind like the prospect of a hanging," Secretary of State John Kerry told a congressional hearing on Tuesday.
A CNN/ORC International poll released Monday said 59% of respondents opposed congressional authorization of military action, while 72% said American strikes would achieve no significant goals.
Critics call the situation faced by Obama his own doing for a confused Syria policy that he has never fully explained.
"There's a degree of incoherence that I have never seen the likes of," veteran Republican Sen. John McCain of Arizona told CNN on Tuesday.
A senior administration official involved in Syria policy pushed back against such criticism on Tuesday, saying skepticism about Obama's call for a military response was understandable while noting that the new diplomatic discussion meant that "today is better than yesterday."
"We would rather have a situation where it is possible there is a diplomatic solution in the offing than one with no choice but to pursue military action," the official said on condition of not being identified.
Obama's reluctance on Syria
For two years, Obama resisted calls by conservative hawks such McCain to back rebels fighting the al-Assad regime, saying the United States sought no role in the Syrian civil war.
When evidence of chemical weapons use emerged earlier this year, and Hezbollah fighters from Lebanon helped al-Assad's forces gain the upper hand, Obama agreed in June to provide military aid to the rebels.
The August 21 attack clearly crossed a "red line" he declared earlier against chemical weapons use, prompting his decision for what he hoped would be an international military response against Syria.
However, Britain's Parliament voted against joining a military response, denying Obama a normally reliable ally. He then decided to seek authorization from Congress to provide political cover and buy time to build a broader international coalition.
Now legislators from both parties are threatening to oppose a resolution authorizing a military response, and Obama has asked for time to let the diplomatic process play out.
Kerry heads to Geneva on Thursday for talks with his Russian counterpart, who first offered his government's proposal Monday after Kerry earlier said Syria's turning over its chemical weapons was the only way to avoid a U.S. attack.
Syria agreed Tuesday to the Russian proposal, with Foreign Minister Walid Moallem saying his government was ready to disclose the location of its chemical weapons, halt production, and show its facilities to representatives of Russia, the United Nations, and other unspecified states.
At the same time, Russian President Vladimir Putin said Tuesday that "all of this will only mean anything if the United States and other nations supporting it tell us that they're giving up their plan to use force against Syria."
"You can't really ask Syria, or any other country, to disarm unilaterally while military action against it is being contemplated," Putin said in an interview with a Russian television network.
Obama: Threat of strikes still critical
For his part, Obama sought to persuade Americans of the opposite -- that the diplomatic stirrings by Russia and Syria occurred because of the credible threat of a military attack intended to deter Syria from using its chemical weapons again.
The president has not said whether he would launch strikes without the support of Congress.
Meanwhile, a bipartisan group of eight senators is working on an alternative resolution to the one authorizing military action already passed by the Senate Foreign Relations Committee. It would include "guidelines, reporting process and benchmarks that have to be met," McCain told CNN.
On the House side, Democratic Rep. Chris Van Hollen of Maryland said he was working on a version of a resolution that would authorize a military response if the diplomatic process failed to yield an acceptable result in 30 days.
The Obama administration has launched a sweeping lobbying effort, with the president meeting on Capitol Hill on Tuesday with senators from both parties as part of a series of classified briefings, hearings and other consultations on the Syria issue.
Since Friday, the administration has spoken with at least 93 senators and more than 350 members of the House, a White House official said Tuesday.
Despite such outreach, indications were that the congressional push wasn't working.
Sen. Mitch McConnell, the top-ranking Republican in the Senate, announced Tuesday he will vote against authorizing military action on Syria.
So did Democratic Sen. Ed Markey of Massachusetts, who won the seat vacated by Kerry when he became secretary of state.
A running CNN vote count showed most members of Congress remained undecided, with significant opposition in both chambers among the much smaller numbers who have announced their decision leaving the outcome in doubt.
CNN's Jim Acosta, Josh Levs, John King, Ted Barrett, Kevin Bohn, Stephanie Halasz and Jill Dougherty contributed to this report.