WASHINGTON — In the high-stakes battle over health care, a growing chorus of liberal activists is aiming its sharpest firepower against Democratic senators who they accuse of being insufficiently committed to the cause.
The attacks — ranging from tart news releases to full-fledged advertising campaigns — have elicited rebuttals from lawmakers and sparked a debate inside the party over the best strategy for achieving President Barack Obama’s top priority of a comprehensive health-system overhaul.
The rising tensions between Democratic legislators and constituencies that would typically be their natural allies underscore the high hurdles for Obama as he tries to hold together a diverse, fragile coalition.
Activists say they are simply pressing for quick delivery of “true health reform,” but the intraparty rift runs the risk of alienating centrist Democrats who will be needed to pass a bill.
In recent days, left-leaning bloggers and grassroots organizations such as , Health Care for America Now and the Service Employees International Union have singled out Democratic Sens. Ben Nelson of Nebraska, Mary Landrieu of Louisiana., Ron Wyden of Oregon, Arlen Specter of Pennsylvania and Dianne Feinstein of California for the criticism more often reserved for opposition party members.
As health care moves from electoral rallying cry to the work of legislating, Obama finds himself caught between his campaign foot soldiers and the elected politicians who will vote.



