Unlike the bipartisan group, Shaheen has already drafted the legislative text of her proposal, which she has offered as an amendment to the pending use-of-force resolution.

She planned to begin calling colleagues Tuesday morning in search of co-sponsors.

Under Shaheen’s proposal, President Obama would have authorization to launch strikes if “Syria is not taking credible and concrete steps toward the removal and destruction of Syria’s chemical weapons stockpile,” according to text provided by a Senate aide.

Shaheen’s amendment does not yet state how many days after its enactment Syria would have to show progress toward eliminating its chemical stockpile to avert an attack.

— This story was updated at 11:55 p.m.