The White House brushed aside a growing list of political and legal threats to its signature health care law on Friday, vowing to pass the torch to Obamacare’s allies so that Americans can seek taxpayer-subsidized coverage for “generations” to come. President Obama’s chief of staff, Denis McDonough, extolled the 2010 overhaul and grassroots aides who have herded millions into the law’s web-based exchanges, and will be critical to the law’s survival beyond Mr. Obama’s tenure. He then scolded critics who’ve tried to kneecap the reforms through Congress and the courts. “Despite the efforts to defame, to defund and to discard the Affordable Care Act, the truth is that it has served as a steward of freedom, for it’s liberated millions of Americans from fear and provided them with a peace of mind,” he said at a D.C. summit hosted by Enroll America, a nonprofit that promotes Obamacare’s exchanges. Roughly 20 million Americans have gained health coverage through the law’s exchanges and the expansion of Medicaid, the government-run insurance program for the poor, in 31 states and D.C. The law also allowed young adults to stay on their parents’ plans until age 26. Mr. McDonough spoke optimistically about the years beyond this presidency, predicting the law will not add to deficits and generate “substantial savings that grow and grow over time” by slowing year-to-year growth in health spending. “We must strengthen and institutionalize the enrollment capacities of our communities, so that they are empowered to enroll Americans for months, years and generations to come,” he said. Yet Republicans say cracks in the law are already showing. Insurers facing a sicker-than-expected customer base are preparing double-digit rate hikes for Obamacare customers, to be announced in the coming months, handing Republican critics another talking point as they try to sync up with de facto GOP presidential nominee Donald Trump and convince voters to accept a repeal of the 2010 law. At the same time, House Republicans are brainstorming ideas for a long-awaited replacement that relies on market incentives and health savings accounts that put patients in charge of their health dollars. …