With news quickly spreading that Army Gen. Martin Dempsey has likely been selected to become the next chairman of the Joint Chiefs of Staff, it’s time to make a prediction: Even with Marine Gen. James Cartwright likely retiring by the end of the summer, the military will likely retain four four-star Marine generals. That much seems obvious, even as speculation swirls over who will replace Cartwright as JCS vice chairman. No Marines are believed to be in serious contention for the four-star position, which Cartwright has filled since Aug. 31, 2007. Instead, rumors have centered mostly on Air Force Gen.…