When Rushern L. Baker III, Prince George’s county executive, announced he wanted a billion-dollar casino built on the banks of the Potomac River, he wasn’t quite sure what he was getting into. Baker (D) had opposed slots during a decade as a Maryland state delegate and was taking a considerable political risk as the biggest cheerleader for bringing gaming to Prince George’s. His views had changed in the 14 months since becoming county executive, and he saw a “high-end” destination much like what’s available in Las Vegas as a risk worth taking: It would help him expand the county’s tax base, keep dollars from county gamblers at home, and draw tourism and economic development. “I didn’t know what a billion-dollar casino looked like,” Baker said in an interview last week . “But I knew a billion dollars was a lot of money.” Anyone willing to make that kind of investment would not be building a “slots barn.” It would be a resort with upscale restaurants, boutiques and an exclusive entertainment experience. There were some doubters, but soon National Harbor developer Milt Peterson came on board, and MGM chief executive Jim Murren joined in an arduous and expensive campaign to bring th...