"Republicans can't stress enough that extremists are screaming 'Doomsday!'" reads a leaked memo from the U.S. House of Representatives' Republican Conference communications office to GOP members. The memo isn't referring to the Middle East -- it's offering advice on how to dismiss environmental issues raised by Democratic challengers. Suggestions include: "Global warming [3] is not a fact," "links between air quality and asthma in children remain cloudy," and the Environmental Protection Agency is "exaggerating" water pollution claims. The House memo echoes an earlier warning from GOP pollster Frank Luntz [4] that the party is "most vulnerable" on environmental issues.