Most travelers probably don't know or care that a private-sector company is behind the enrollment process for TSA PreCheck. They might soon. To expand the program's membership, TSA last month said it expected two new authorized enrollment providers to begin PreCheck services by year-end. This won't change how members use the program to get through airport security faster, but it may give them choices on how to enroll, how much they pay and whether they'll get other benefits. It also may present new possibilities for companies looking to organize on-site enrollment events . . .