There’s been lots of buzz about President Joe Biden’s health care agenda and which proposals he’s going to make a priority. But almost nobody is talking publicly about an idea that could do a ton of good: Getting health insurance for the low-income people who are part of what’s come to be known as the “Medicaid gap.” There are about 4 million of these Americans, according to estimates ― many of them food servers or retail clerks, parts of the child care workforce or, in some cases, among the ranks of the unemployed. And they were supposed to have health insurance already, thanks to the Affordable Care Act, which gave states extra funding to cover them through Medicaid. But it hasn’t worked out that way in roughly a dozen states, all places where Republican officials have refused to take the federal money. Those states still have their older Medicaid eligibility guidelines, which restrict enrollment to narrower groups of the population. With little reason to think GOP officials in these states will change their minds, it’s up to Democrats in Washington to come up with an alternative ― a way of insuring these 4 million people through some kind of new federal initiative.