http://www.publicpolicypolling.com/main/2015/08/general-election-tight-in-iowa.html"The strongest Republican against Clinton in the state is Ben Carson, who leads her 44/40. The other three GOP hopefuls ahead of Clinton all lead her by just a single point- Mike Huckabee at 44/43, Scott Walker at 44/43, and Marco Rubio at 43/42.
The Republicans who fare the worst against Clinton are Jeb Bush who trails by 4 at 44/40, and Rand Paul and Donald Trump who each trail by 3 at 43/40. The rest of the GOP hopefuls each trail Clinton by 2 points- Ted Cruz at 44/42, Carly Fiorina at 42/40, and Chris Christie and John Kasich each at 41/39."
