RICHMOND, Va. — Lt. Gov. Justin Fairfax of Virginia on Monday emphatically denied a woman’s claim that he sexually assaulted her in 2004, suggesting that Gov. Ralph Northam’s supporters were trying to block his ascent to the governorship at a moment Mr. Northam is besieged by demands that he resign over charges of racism. “Does anybody think it’s any coincidence that on the eve of potentially my being elevated that that’s when this uncorroborated smear comes out?” Mr. Fairfax told reporters surrounding him in the rotunda of the state capitol about whether he believes Mr. Northam, a fellow Democrat, was...