Many of the millions of people who lose Medicaid coverage, either because they no longer qualify or because they are otherwise dropped from the state’s rolls, sometimes mistakenly, are likely to discover they are uninsured only when they next seek medical care, such as when they visit a clinic or go to a pharmacy to refill a prescription.

And that’s in a country where an inhaler can cost $50 to $100, a doctor’s visit typically costs over $100, and a hospitalization for Covid-19 can run tens of thousands of dollars.

On top of all that, the enhanced government subsidies to buy Affordable Care Act health plans — provisions of the American Rescue Plan that make insurance more affordable for low and even some middle-income people — expire at year’s end. For example, premiums for a silver level health plan that would normally cost $560 a month, on average, were reduced to just $390 with the extra government support for someone earning $55,000 a year, resulting in an annual savings of over $2,000.

When those enhanced subsidies expire, many lower-income Americans could be left with the prospect of paying double for health coverage.

The Build Back Better Bill, which passed the House in November, would have extended the more generous subsidies for purchasing A.C.A. health plans. But the bill was declared “dead” by Senator Joe Manchin of West Virginia, this year, who refused to support it. Now Democratic leaders are hoping to negotiate a slimmed-down version of the bill, but it’s unclear whether a bill will materialize with the provision in it.

It is a perilous time to throw low- and middle-income Americans off the insurance cliff: A new Omicron subvariant is spreading, and a program that provided coronavirus testing and Covid treatment at no cost to the uninsured expired in March because the government ran out of funds to support it. Another program that provided vaccination at no cost to patients is set to end this month.