From the Amtrak website:

Empire Builder, Trains 7/27/807 & 8/28/808

Service by the Empire Builder on CP Railway between St. Paul and Chicago, suspended since June 10 due to flooding in Wisconsin, has resumed using a Union Pacific detour route, effective June 27.

You can get a 30-day USA Rail pass that allows unlimited coach travel anywhere in the US for about $550--your friend would travel Portland to Chicago on the Empire Builder (about 45 hours), then change trains for Detroit--Haven't been to the Portland station, but the contrary to what JoSuC claims, the Chicago station is a great bldg in right in downtown. Rather than going to Detroit, people usually go to the relatively new station in Dearborn, which is more convenient than the Detroit terminal for a variety of reasons.

If one is so inclined, it is possible to upgrade from coach to a sleeping car on the Empire Builder--