TSA already monitors Amtrack:
http://www.cnn.com/2012/02/06/opinion/don-phillips-tsa-vipr-...
Due to the broad description of the organization's purpose, it gives them overreaching powers allowing them to secure any mode of transportation. This has led to the TSA expanding its presence and showing up at NFL games:
http://www.huffingtonpost.com/christopher-elliott/the-tsa-wa...
Edit: For those commenting about NFL game presence without reading the linked article...
> Few people know that $105 million of their taxpayer dollars are going to fund
> 37 VIPR teams in 2012, whose purpose is to "augment" the security of any mode
> of transportation. They don't realize that these VIPR teams can show up
> virtually anytime, anywhere and without warning, subjecting you to a search
> of your vehicle or person.