Nearly two dozen Pennsylvania residents, interviewed recently by Abby Goodnough of The Times, said they were opposed to President Obama’s health care reform law. Though almost all of them would benefit from it, they expressed fears about a loss of control over their health care that is nowhere in the law. For Op-Ed, follow @nytopinion and to hear from the editorial page editor, Andrew Rosenthal, follow @andyrNYT.There are two reasons for this situation, which is repeated around the country. Business groups allied with Republicans have spent $235 million on television ads attacking the law with false accusations, with the vigorous aid of Mitt Romney and his campaign. Meanwhile, Democrats and the Obama campaign have been amazingly reluctant to speak up for the president’s biggest accomplishment and tell voters what’s in it. The president has not even capitalized on his victory in the Supreme Court last week over his opponents’ attempt to dismantle the law on constitutional grounds. He listed some of its benefits in a low-key East Room speech after the ruling, and the campaign has sent out several direct-mail fliers on the subject to women. But the campaign has broadcast no television ads about health care, except for one in Spanish. Jack Lew, the White House chief of staff, said on “Fox News Sunday” that it was time “for the divisive debate on health care to stop,” suggesting Democrats want to move on. Mr. Lew might consider going to a swing state and turning on the television because the debate isn’t going to stop. Republicans are happy to continue it with obvious propaganda like “Obamacare is the largest tax increase in U.S. history.” Countering this attack and, more important, building a foundation of support for a vastly important social change, will require the president and other Democrats to spend more time and more money explaining the law’s benefits, and pointing out that Republicans have no useful ideas to replace it. The White House has been halfhearted in its sales pitch almost from the beginning of Mr. Obama’s administration. Polls showed that many middle-class voters, comfortable with their own insurance, weren’t particularly interested in a new social program that extended coverage to 30 million uninsured people, many of them poor. Beyond simple decency, that’s a huge benefit to society as a whole, improving public health and reducing expensive emergency care that everyone pays for. In uncertain times, as well, anyone can suddenly lose health insurance. But that case was never forcefully made, and Republicans exploited the complexity of the law to persuade casual listeners that, as the House speaker, John Boehner, claimed on Sunday, “this is government taking over the entire health insurance industry.” Expanding coverage is an idea worth defending, particularly when Republican leaders acknowledge that they have little interest in doing so, as Senator Mitch McConnell, the Republican leader, did on Sunday. And there many other aspects of the law for which Democrats should use a megaphone: an end to the Medicare “doughnut hole”; a huge expansion of coverage for mental health; an end to lifetime and annual limits on coverage and of rejection because of a pre-existing condition; a requirement that medium and large businesses provide essential coverage and pay for 60 percent of it; free access to preventive care like immunizations and mammograms. The campaign committee for House Democrats, with little money, is making telephone calls going after Republicans for their votes to repeal the law and loosen the reins on insurance companies. It’s past time for the White House and the Obama campaign to set aside their diffidence and begin playing an equally aggressive offense.