For decades, the federal government has funneled big-ticket grants to local communities to help them take on ambitious construction projects to expand public transit. The grants, sometimes in the billions of dollars, have funded new railroad tracks, train stations and roads rebuilt for modern bus service. Today, they’re funding extensions of the Second Avenue Subway in New York and the Red Line in Chicago, as well as the Gateway Tunnel under the Hudson River and bus infrastructure in Indianapolis and San Antonio.But since President Trump returned to office, the Federal Transit Administration has not signed a single new agreement under...