Polio was almost eradicated. Then came the coronavirus. Then came a threat from President Trump.

For decades, the United States has worked with the World Health Organization and others to quash polio, beating back to near extinction a merciless disease that once paralyzed hundreds of thousands of children each year. That progress is in danger as the pandemic forces health-care providers to suspend door-to-door vaccination campaigns that have slashed the number of infections. … “As soon as you let off, you get cases,” said Andrew Noymer, an associate professor of population health at the University of California at Irvine.