Agreed--though progressives deny it.
source: Carpe Diem
The chart above displays GDP at purchasing power parity (PPP) per capita in 2008 using data from the CIA World Factbook (data available here) for various European countries, the European Union as a group, Japan, and the U.S. The chart also shows an estimate of GDP per capita for America's poorest state of Mississippi ($34,968), adjusted for purchasing power by applying a factor of .7439 to U.S. per capita GDP adjusted for PPP of $47,000, based on Mississippi's unadjusted GDP per capita compared to the U.S. average (data here).
On a PPP basis, all European countries in the graph except the U.K. have per capita GDP below America's poorest state. In other words, if Italy, France, or Germany left the European Union and joined the U.S., they would be the poorest of the U.S. states, and the same would apply to the European Union as a group, and the same would apply to Japan.