ABC News' Teddy Davis Reports: If an immediately available — no trigger — public option makes it to President Obama's desk, the member of Congress who may deserve the most credit for making it happen is Sen. Chuck Schumer. The New York Democrat came up with the idea of a public option with a state opt out clause just a few short weeks ago. Schumer's proposal, which was publicly embraced on Monday by Senate Majority Leader Harry Reid, D-Nev., is a more liberal variation of an idea originally developed by moderate Democratic Sen. Tom Carper of Delaware. Carper wanted to give states the option of choosing to create their own state-based, or regionally-based, public insurance options. While Carper's proposal was met with positive reviews from some conservative Democrats, liberals remained concerned that state-based public options wouldn't have the bargaining power of a nationwide public plan. Even more importantly, Carper's proposal would have placed the onus on the advocates of a public option. For this reason, the Carper proposal failed to catch on with progressive Democrats. It was at this point that Schumer came up with the idea of inverting Carper's proposal: instead of giving states the option of opting in, give states the option of opting out. "The goal was to make it a default choice available to anyone who wants it," said a Democratic Senate aide. "Even if you have a Republican governor and live in a Red State, the public option will be available right away and you can fight to keep it." Under Schumer's proposal, legislation would have to be passed by the state legislature and signed by the governor in order for a state to remove itself from the national public plan. Progressives, who had been deeply dismissive about Sen. Olympia Snowe's, R-Maine, proposal to create a public option only as a fallback if affordable private insurance was not available, quickly warmed to the state "opt out" proposal. Conservative Democrats, however, remained a tougher sell. Carper himself never officially signed onto the Schumer proposal, preferring his own more moderate version. But about a week and a half ago, Schumer altered his lobbying strategy with conservative Democrats: instead of asking if they would support a public option with a state opt out clause, Schumer simply began asking if it would be "a deal breaker" for them. What he learned, according to a Senate Democratic aide, was that his fellow Democratic senators were not "put off enough" by the proposal to say that they would "join a Republican filibuster." Once the Schumer proposal showed that it was capable of winning the support of liberals and moderates without provoking an immediate backlash from conservative Democratic senators, Reid decided to "roll the dice" and include a public option with a state opt out clause in the legislation which will reach the Senate Floor. Although Monday was a big step forward for advocates of a public option, there are still considerable hurdles ahead. While Reid believes he can hold 60 Democratic senators together behind a motion to proceed on a bill which includes Schumer's proposal, Democrats did – at least temporarily – lose the support of Snowe, heretofore their lone Republican supporter, and there are still at least three Democratic senators — Sen. Blanche Lincoln of Arkansas, Sen. Ben Nelson of Nebraska, and Sen. Mary Landrieu of Louisiana. — who have not committed in public to backing the motion to proceed. These senators maintain that they want to see the specific legislation before committing their votes in public. "It's a great day. It's a giant step forward. But it aint over 'til the fat lady sings," said Schumer on Monday evening while appearing on MSNBC's "Countdown with Keith Olbermann."