Washington ? Frustrated liberals have a question for President Barack Obama and Democratic lawmakers: Isn’t it time the other guys gave a little ground on health care? What’s the point of a bipartisan bill, they ask, if we’re making all the concessions?

A case in point:

Sen. Charles Grassley, a key Republican negotiator on health care, was on a winning streak as Congress recessed for August, having wrung important concessions from Democrats, including an agreement to back away from a government plan to compete with private insurers.

How did Grassley reciprocate? With an attack that struck Democrats as stunning and baseless. Grassley told an Iowa crowd he would not support a plan that “determines when you’re going to pull the plug on Grandma.” The remark echoed conservative activists who wrongly claim a House health care bill would require Medicare recipients to discuss their end-of-life plans with doctors.

For liberals supporting far-reaching changes to the nation’s health care system, it was another sign that months of negotiations have been a one-way street. It’s time to move on without Republicans, they say.

On Tuesday, liberals were fuming over Obama’s recent remarks suggesting he might also yield on the federally run insurance option he’s been promoting. Many saw it as a huge concession that could leave them with nothing more than watered-down insurance cooperatives.

But the Senate’s second-ranking Republican, Jon Kyl of Arizona, dismissed even such co-ops as a “Trojan horse” leading to government control of health care.

Many liberals are fed up.

“It is clear that Republicans have decided ‘no health care’ is a victory for them,” Andy Stern, president of the Service Employees International Union, said in an interview. “There is a point at which bipartisanship reaches a limit, and I would say it’s reaching that limit.”

The growing liberal unhappiness sets a difficult stage for Obama this fall. Political pragmatists want him to keep seeking a middle ground that will attract at least a few Republican lawmakers as well as moderate Democrats who could prove crucial to passage in the House and Senate. Even modest achievements, such as preventing insurers from refusing to cover pre-existing medical conditions, would allow Obama to claim a victory and perhaps try for more later, they say.

Liberal activists say there’s no point in the Democrats winning the House, Senate and White House unless they use their clout to enact the major measures that Obama campaigned for — with or without some Republican support.

For now, Obama seems on the defensive. He spent valuable time this month knocking down claims that Democratic plans could lead to euthanasia of the elderly. And his chief spokesmen spent much of Monday and Tuesday insisting that Obama still supports a government-run health insurance option despite mixed signals from the administration.

On Saturday, Obama told a Colorado crowd, “The public option, whether we have it or we don’t have it, is not the entirety of health care reform. This is just one sliver of it.”

While liberals are discouraged, the endgame remains unclear. Some still hope that Obama and congressional Democratic leaders will use all their parliamentary powers — which could prove especially divisive in the Senate — to pass a far-reaching bill that would include a public option for health insurance and more palatable consumer costs for prescription drugs and other needs.

The pivotal decisions will be made this fall, with administration officials saying the debate cannot lapse into the midterm election year of 2010.