Read about this in Amtrak the history and politics of a american rail road David C Nice
The Inter American was the train which later became the TX Eagle. In 1979, Amtrak suffered a major service reduction when four long distance trains were abolished. The IA was one which was on a possible to-do-away list. Because of support from the powers in DC along the route of that train, the IA survived while the Chicago-Houston Lone Star was killed off. The Lone Star had higer ridership, stronger route support but little support from good ole DC.
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The original Inter-American ran from Ft Worth to Laredo, ATSF to Milano TX where it turned on a very sharp interchange track to the MoP. I have picures of a yellow UP E unit and 3 Santa Fe coaches making this turn in '72 or '73. To those of us railfanning in TX at the time it was known as “The Tamale”