McLEAN -- A Fairfax County judge has ruled that key components of Virginia's drunken-driving laws are unconstitutional, citing an obscure, decades-old U.S. Supreme Court decision that could prompt similar challenges nationwide. Virginia's law is unconstitutional because it presumes that an individual with a blood-alcohol content of 0.08 or higher is intoxicated, denying a defendant's right to a presumption of innocence, Judge Ian O'Flaherty ruled in dismissing charges against at least two alleged drunken drivers last month. As a district judge, O'Flaherty's rulings do not establish any formal precedent, but word of the constitutional argument is spreading quickly among the defense...