SAN DIEGO — The coronavirus pandemic has exacerbated problems for the U.S. Postal Service and sparked a debate in Washington, D.C., that could carry major ramifications for the November general election.The U.S. Postal Service, or USPS, has long been America’s most popular public agency; a recent poll by the Pew Research Center found that 91% of Americans had favorable opinions about the agency.Nevertheless the agency has frequently faced financial challenges, which have escalated during the pandemic, as revenue plummeted and mail volume dropped more than 30% from last year.Federal officials s…