before obamacare, it could be hard to buy your own insurance if you<u+2019>d already had a health problem like cancer. an insurance company might have decided not to sell any insurance to someone like you. it might have agreed to cover you, but not cover cancer care. or it might have offered you a comprehensive policy, but at some incredibly high price that you could never have paid. donald j. trump says he wants to do away with much of obamacare, but he has signaled that parts of the law that banned those practices are good policy he<u+2019>d want to keep. <u+201c>i like those very much,<u+201d> he told the wall street journal last week about the law<u+2019>s rules that prevent discrimination based on pre-existing conditions. the pre-existing conditions policies are very popular. nearly everyone has relatives or friends with illnesses in their past <u+2014> cancer , arthritis , depression, even allergies <u+2014> that could have shut them out of the individual insurance markets before obamacare, so it<u+2019>s an issue that hits close to home for many americans. but keeping those provisions while jettisoning others is most likely no fix at all. those policies that make the insurance market feel fairer for sick americans who need it can really throw off the prices for everyone else. that<u+2019>s why obamacare also includes less popular policies designed to balance the market with enough young, healthy people. imagine you<u+2019>re that patient with cancer. you really want health insurance, and you<u+2019>re probably willing to pay a lot to get it. if the law requires insurance companies to offer you a policy, you are very likely to buy it. now imagine you<u+2019>re a young, healthy person without any health problems. your budget is tight, and health insurance is expensive. you might decide you<u+2019>ll be fine without insurance, since you can always buy it later, when you<u+2019>re the one with a pessimistic diagnosis. before obamacare, several states tried policies like this, and required insurance companies to sell insurance to everyone at the same price, regardless of health histories. the results were nearly the same everywhere: prices went way up; enrollment went way down ; and insurance companies fled the markets. some states hobbled along with small, expensive markets . some experienced total market collapse and repealed the policies. prices in those markets typically became so high that they were really a good deal only for people who knew they<u+2019>d use a lot of health care services. and the sicker the insurance pool got, the more the companies would charge for their health plans. the health law attempts to broaden the pool by offering financial assistance to middle-class people. by limiting how much people can be asked to pay for insurance, the law<u+2019>s subsidies help make the purchase more attractive for healthier customers. that<u+2019>s the law<u+2019>s carrot. then there<u+2019>s the stick: the law says that if you don<u+2019>t buy insurance, and you could have afforded it, you have to pay a fine. that rule is designed to discourage people from gaming the system by waiting until they<u+2019>re sick. the mandate remains the law<u+2019>s least popular provision. new york is a great case study. before obamacare, it had the pre-existing conditions policy, but without subsidies or a mandate. when the obamacare rules kicked in, premiums there went down by 50 percent . this year, obamacare premiums have risen substantially <u+2014> an average of 22 percent around the country <u+2014> leading many experts and politicians to question whether the law<u+2019>s incentives were strong enough . some, including hillary clinton, have argued that the government should sweeten the carrot, by making the subsidies more generous. others have said that the stick should sting more by forcing the uninsured to pay a bigger penalty for sitting out of the market. republican politicians have tended to criticize both of the incentive provisions. the subsidies have been attacked as excessive government spending. the mandate has been criticized as an inappropriate use of government power. both have been the subject of big supreme court cases challenging the law. both would have been eliminated under a bill passed by congress but vetoed by president obama last year. taking away those unpopular pieces of the law and keeping the popular pre-existing conditions piece might seem like a political win. but it would result in a broken system. when mitt romney was devising the massachusetts health reform law that would become the model for obamacare, he hoped to set up a marketplace for health plans with some financial assistance for low-income people to buy insurance. what he didn<u+2019>t want was a mandate. then jonathan gruber, an m.i.t. economist who had calculated the results, showed him the numbers: his plan would cover only a third of the uninsured and cost two-thirds as much as an identical plan with a mandate. mr. romney embraced the mandate. when barack obama ran for president in 2007, he, too, advocated a market-based health reform system. he, too, said he did not support a mandate . then he became president, and economists brought him the numbers . by the time the affordable care act passed, he had changed his mind. we<u+2019>ll see what happens when the economists bring the numbers to mr. trump. his transition website suggests that he might develop a different solution to the problem: a special, separate insurance market just for sick people. but that plan is different from the more modest amendments to the affordable care act he described to the wall street journal. it won<u+2019>t be easy to keep the basic architecture of obamacare while plucking out its least popular pieces. (another provision that mr. trump says he likes, the requirement that insurers cover young adults on their parents<u+2019> policies, would be easier to save.) last year, i spoke with mark hall, a law professor at wake forest university who studied the states that had tried pre-existing conditions bans before obamacare. one of the supreme court cases threatened to wipe out the mandate and the subsidies , and i asked him what would happen if the litigants succeeded. <u+201c>it would be a big mess,<u+201d> he said. the upshot provides news, analysis and graphics about politics, policy and everyday life. follow us on facebook and twitter . sign up for our newsletter . a version of this article appears in print on november 15, 2016, on page a20 of the new york edition with the headline: why keeping only popular parts of the health law won<u+2019>t work. order reprints | today's paper | subscribe
why keeping only the popular parts of obamacare won<u+2019>t work
margot sanger-katz