WASHINGTON — President Joe Biden welcomed a crowd including Illinois Gov. J.B. Pritzker and Highland Park Mayor Nancy Rotering to the White House lawn Monday to showcase a new law meant to reduce gun violence, celebrating “real progress” after years of inaction.But he also lamented the country remains “awash in weapons of war” — with the 16-day-old law already overshadowed by yet another horrific mass shooting.The gun bill, passed after recent gun rampages in Buffalo, New York, and …