National Journal published its first rankings for U.S. Senate races most likely to flip parties in the 2018 election cycle,  and ranked Nevada’s Dean Heller as the most vulnerable Republican on the map,  and the fourth most likely incumbent Senator to lose their seat next year.  National Journal says Heller is the top target of Democrats, one cycle after the party carried Nevada at the presidential level, held an open Senate seat, and flipped two House seats.