A crazed gunman shot two National Guard troops in a cowardly “ambush”-style attack — leaving them in critical condition — just blocks from the White House on Wednesday in what’s now being investigated as a terror attack, according to law enforcement sources and officials. The gunman — identified by sources as Afghan national Rahmanullah Lakanwal, 29 — was lying in wait before rounding the corner and 17th and I Streets around 2:15 p.m. and ambushed the pair of Guard members and opened fire, authorities and sources said. Lakanwal, who has a Washington state address, came to the US as part of the 2021 Afghanistan withdrawal, sources said.