Many of the nation's 3.5 million teachers found themselves feeling under siege this week as pressure from the White House, pediatricians and some parents to get back to physical classrooms intensified -- even as the coronavirus rages across much of the country.On Friday, the teachers' union in Los Angeles, the nation's second-largest district, demanded full-time remote learning when the academic year begins on Aug. 18, and called President Donald Trump's push to reopen schools part of a "dangerous, anti-science agenda that puts the lives of our members, our students and our families at risk."Teachers say crucial questions about how schools will stay clean, keep students physically distanced and prevent further spread of the virus have not been answered. And they feel that their own lives, and those of the family members they come home to, are at stake."I want to serve the students, but it's hard to say you're going to sacrifice all of the teachers...