"Everyone who positions themselves as a progressive needs to think very hard about what their vote will mean down the road," said Anna Galland, executive director of MoveOn.org.
At the same time, a large delegation of members representing the influential American Israel Public Affairs Committee, the pro-Israel lobbying group with strong ties to congressional Democrats, plans to press lawmakers on Capitol Hill next week to approve the resolution.
The vote could carry implications beyond this year. House Democrats who represent liberal districts might face primary challenges if they support the resolution. The votes could figure prominently in several key Senate races crucial to Democrats' effort to maintain control of the chamber during Obama's final two years.
Incumbents in two closely watched races — Sens. Mary Landrieu of Louisiana and Mark Begich of Alaska — remain undecided. But Sen. Mark Pryor of Arkansas, running for a third term, said in a statement Saturday that "at this time" he can't support the resolution to intervene in Syria that lawmakers are expected to consider next week.
Among potential 2016 presidential candidates, Clinton said through an aide that she supported Obama's efforts in Congress. As secretary of state she urged the administration to intervene in Syria, and a speech in Philadelphia on Tuesday could give the former first lady the opportunity to discuss a potential U.S. response. Maryland Gov. Martin O'Malley told reporters last week that there was a need for a "clear understanding of what it is exactly this mission would hope to accomplish."
Wrapping up a trip to Sweden and Russia, Obama will try to make a full-court press next week, addressing the nation on Tuesday while his administration fans out to briefings and meetings with wavering lawmakers.
Associated Press writers Alan Fram in Washington and Thomas Beaumont in Des Moines, Iowa, contributed to this report.
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