WASHINGTON (Reuters) - The trillions of dollars in cash and loans unleashed by the Federal Reserve and U.S. political leaders in recent weeks is meant to build a financial bridge for the country to get beyond the coronavirus pandemic and restart the economy with little or no long-term damage. But that mammoth effort is still likely to leave millions of additional Americans unemployed for an extended time, according to new economic forecasts that see the U.S. unemployment rate not just spiking to Depression-era levels in coming weeks, but remaining above a relatively high rate of 6% through the end of 2021.