WASHINGTON (Reuters) - President Joe Biden's Justice Department is stepping up its fight against a new state law in Missouri that aims to invalidate many federal gun regulations, saying the measure has impeded law enforcement efforts to work with state and local police and is also unconstitutional. On Wednesday, the Justice Department filed a statement of interest in an ongoing lawsuit in Cole County, Missouri, saying the state's Second Amendment Preservation Act, also known as "HB85," should be declared unconstitutional and that the court should issue a injunction barring its enforcement. "HB85 is legally invalid. Under the United States Constitution’s...