By Gram Slattery WASHINGTON (Reuters) -President Joe Biden and former President Donald Trump headline rallies in New York and Florida, respectively, on Sunday to fire up voters two days before a tight midterm election in which Republicans are pushing to flip both chambers of Congress. Nonpartisan forecasts and polls show Republicans are heavy favorites to win control of the House of Representatives, with the Senate a toss-up. Control of even one chamber would allow Republicans to stymie Democrat Biden’s legislative agenda and launch potentially damaging investigations. In recent weeks momentum…