Midterms Give Parties Chance for Sweeping Control of States

It was over 100 degrees here the other evening, but inside a buzzing office tucked away on a stretch of gun stores and pornography shops, Democrats were staring into computer screens and talking urgently into cellphones. The stakes were high: The Nevada Senate, which Democrats control by a single seat, could very well shift into Republican hands after November.

“Hi, this is Justin Jones; I’m your state senator,” said Mr. Jones, a Democrat who won by only 301 votes two years ago. “We have a really important election campaign coming...