Democrats proposing an overhaul of the American health care system have gotten themselves locked in a box around the question of affordability. This is not the question of whether the proposed health care legislation is affordable for taxpayers and the federal government -- an issue that seemed to be answered when the Congressional Budget Office said the Senate Finance Committee's bill would eventually help reduce federal budget deficits. The affordability question vexing Democrats is whether those with moderate income will be able to afford health insurance, even with the subsidies the legislation would provide and all sorts of new rules aimed at controlling costs. Because the legislation would require nearly all Americans to obtain health insurance, affordability is a potentially serious political issue. That is particularly so because most people would incur a financial penalty -- payable along with income taxes -- if they did not obtain coverage. Sen. Charles E. Grassley of Iowa, the senior Republican on the Finance Committee, last week attacked the requirement to have insurance, the so-called individual mandate, as potentially imposing a crippling penalty of $1,500 on a family earning as little as $25,000 a year. 'It's a pretty heavy burden for low-income families,' Grassley said in committee debate. Some liberal Democrats are already suggesting that the legislation may not be worth adopting if it will end up forcing Americans to buy health coverage they really cannot afford. 'I am sympathetic, and I understand the concerns, and I appreciate as well the political volatility around the question of mandating or requiring coverage,' said Sen. Debbie Stabenow, D-Mich., who is also on the finance panel. 'The big question we have all grappled with is how do you make sure everybody is in, and that's a tough one. It comes down to whether or not ultimately in this bill we can say this is affordable for people.' There are two obvious ways of making coverage more affordable, and neither is workable. One would be to sharply reduce the cost of health care across the board, thereby limiting the cost of insurance. This is a chief aim of the Democrats' bill, but it would require sweeping improvements in efficiency, including higher-quality, lower-cost treatment and better use of technology -- all goals of the legislation, but not about to happen anytime soon. The other obvious way would be to sharply increase government subsidies to help middle-class people buy insurance. Stabenow, for instance, has proposed capping the amount moderate-income Americans would have to pay for insurance premiums at 6.5 percent of income, with the subsidies paying the balance. The legislation sets that cap on premium costs at 12 percent. President Barack Obama has already sealed the top of the affordability box in his speech to Congress on Sept. 9, saying that he will not accept a health care bill that costs more than $900 billion over 10 years. And subsidies are already the biggest-ticket item. Some top White House officials, however, a potential escape hatch: exempting more families and individuals on the basis of income from the penalty for failing to buy insurance, a fine that for families could run as high as $1,900. The bill proposed by Sen. Max Baucus of Montana, the Finance Committee chairman, would waive the penalty if the cheapest insurance, even with subsidies, would cost 10 percent of a family's income. Lowering the waiver threshold to 5 percent of income is a risky move, because limiting the threat of a penalty could leave more people uninsured, undermining a main point of the legislation. The Congressional Budget Office estimated that while there would be 29 million fewer uninsured people as a result of the legislation, a separate 25 million people would still be uninsured in 2019 -- about one-third of them illegal immigrants. Sparing more people from the penalty would certainly increase the projected number of uninsured, by tempting more people, particularly younger Americans, to continue going without insurance. But White House officials think the number of people willing to risk going uninsured would not rise by much, perhaps 2 million people. The budget office has not issued projections yet, and some Democrats warned that the erosion could be much worse. And in the end, that may be the smallest price to pay to avert what could be a devastating political argument against the Democrats' plan: that working-class Americans would be penalized heavily for not buying insurance they say they cannot afford. Republicans are already blasting the penalty as a new tax and a violation of Obama's campaign promise not to raise taxes on Americans earning less than $250,000. 'The individual mandate in this bill is un-American,' Sen. Jim Bunning, Republican of Ky., said last week. Sen. Ron Wyden, D-Ore., has proposed an amendment that would let states drop the individual mandate if they can get enough people to sign up for insurance without it. 'Individual mandate has always been one of the most contentious aspects of health reform,' Wyden said. Sen. Charles E. Schumer, D-N.Y., has proposed amendments that would reduce the penalty waiver to as low as 7 percent, 5 percent or even only 3 percent of income. As debate resumes this week, Democrats may take a cue from the White House and consider one of them. 