According to Wikipedia here is the history of the route.
The Cardinal is the successor of several previous trains.
The James Whitcomb Riley was introduced by the New York Central on April 28, 1941 as a daytime, all-coach train between Chicago and Cincinnati by way of Indianapolis. It was named after the Hoosier poet James Whitcomb Riley, known for his celebration of Americana. The Riley was retained by the Penn Central (as trains 303 and 304) after its formation from the ruins of the New York Central and Pennsylvania Railroad. Independently, the Chesapeake and Ohio Railway operated the George Washington as its flagship service (C&O trains 1 and 2), running between Cincinnati and Washington, with a section (trains 41 and 42) splitting at Charlottesville and running to Newport News.
Amtrak, upon its 1971 commencement of operations, kept service identical at first. Through Washington-Chicago and Newport News-Chicago coaches began operating July 12, and a through sleeping car began September 8. With the November 14, 1971 schedule, the routes were merged, with the George Washington name being applied eastbound and the James Whitcomb Riley westbound. At the same time the route was extended from Washington to Boston, and was assigned train numbers 50 eastbound and 51 westbound.
On March 6, 1972 the train was rerouted from Chicago's Central Station into Union Station. On April 30 the service was truncated back to Washington from Boston. On May 19, 1974 the George Washington was renamed the James Whitcomb Riley, giving it the same name in both directions. The Newport News section was discontinued June 14, 1976 and the Colonial began running over its former route east of Richmond.
The James Whitcomb Riley was renamed the Cardinal on October 30, 1977, as the cardinal was the state bird of all six states through which it ran. It was discontinued September 30, 1981 (by then having been extended to New York from Washington) and brought back by Congressional mandate on January 8, 1982.
[edit] Train consist
In the early 1990s, the Cardinal ran with the usual Amtrak long-distance consist of 2 F40s/E60 plus several MHC and material handling baggage cars, followed by several Amfleet coaches, an Amfleet lounge, a Heritage diner, 2 or 3 Heritage 10-6 sleepers, a slumbercoach, and finally, a baggage dormitory car. Following the delivery of the Superliner II fleet, however, the Cardinal was re-equipped with Superliner cars in the mid-nineties. As a result, its route was truncated to end in Washington D.C. as the Superliner equipment could not run into Penn Station, New York, due to low clearances there. With the Superliner equipment, the consist would usually be 2 Superliner II sleeping cars, a diner, a Sightseer Lounge, a baggage coach, and a coach.
In 2002, 2 derailments on other routes took numerous Superliner cars out of service. Because of these accidents, insufficient Superliner equipment was available for use on the Cardinal. The Cardinal was re-equipped with a consist of single level long distance cars, including dining, lounge, sleeping and dormitory cars. Fleet shortages since then have shortened the Cardinal further, and at one point, the train was running with two or three Amfleet II coaches and a lounge car. While the sleeping car has been restored, the Cardinal has not had a dormitory car or a diner since. The Cardinal is currently runs with a single engine, three or four Amfleet II long-distance coaches, a single car used as both a diner and a lounge, and a single Viewliner, used as both a crew dormitory and a sleeper.