IN one fell swoop, President Barack Obama must regain the public's attention on health care, explain in detail exactly what he wants in a final deal, unify a restless Democratic Party, prod Congress to get him a bill and bring clarity to a bewildering debate. Obama's decision to give a prime-time speech to Congress Wednesday underscores the stakes for a president, and even a young presidency. He's got to get a law passed in a form that would genuinely help millions of people with their health insurance without having the liberals in his party rebel on him. The White House signaled Thursday that it remains open to compromises necessary to get a deal through Congress. “There are fundamental principles that he believes in,” senior adviser David Axelrod said. “He's not dogmatic about how we get there.” Yet liberals are concerned that means Obama will dilute the bold health care proposals he campaigned for, particularly the inclusion of a government-run insurance plan. And they are letting him know it. In just one example, the Congressional Progressive Caucus, comprising 83 liberal lawmakers, sent Obama a letter Thursday saying a health bill “without a robust public option will not achieve the health reform this country so desperately needs. We cannot vote for anything less.” That idea slams up against overwhelming GOP opposition and the reservations of many centrist congressional Democrats eyeing their next election. So the responsibility is back on Obama. He's the one who opted to let Congress hash out the details and hold out for pragmatic bipartisanship, approaches that stalled and in some ways backfired. He is the one who promised repeatedly that a health care overhaul would pass this year. And he is the one who said that it his job to get a deal done. So after keeping out of the spotlight on health care over the last few weeks, Obama wants to come back big. He chose one of the largest forums any president can grab, the grand stage of an address to Congress. In his favor, the move gives Obama something he had lost from the public: sheer anticipation in what he is going to say. There had been a stretch in summer when Obama was talking nearly every day on health care. The debate got bogged down in messy legislative details and media coverage of angry, if unrepresentative, town halls. Now the White House is promising Obama will offer more specificity and direction. “I don't think anybody will leave Wednesday night without a clear sense of what he proposes, and what health care reform is not,” Axelrod said. Vice President Joe Biden seemed to go even further, promising Obama will clearly spell out what the “pieces have to be and will be.” Obama's critics say that's late in coming. So do many of his supporters, who wonder privately whether the quiet stretch of late has been an opportunity lost. His oft-stated principles on health care have not been enough. Congressional committees made much more progress than in years past, but that now seems more process than progress. “He's now, very late in the game, it appears, maybe going to be a lot more clear about what exactly he wants — and more importantly, what he's willing to fight for,” said Tony Fratto, a former spokesman for President George W. Bush. Since the start of June, Obama has given 25 speeches and statements alone on his health care plan, according to Mark Knoller of CBS News, who keeps a detailed log of presidential activities. And that doesn't include a battery of interviews on the topic. Meanwhile, Obama's approval rating has eroded. A CBS News poll from late August found just 40 percent of people supported his handling of health care. “He's got to take ownership of it in a way that he hasn't quite yet, and he'll only do that by providing the specifics,” said Wayne Fields, a professor at Washington University in St. Louis who studies presidential speechmaking.