When I see this train, the Cardinal at Trenton, it has three Amfleet II coaches, Amfleet diner-lite, and a lone Viewliner. With all due respect Mr. Norman, I just can't figure out how this consist beats out the consist of when this train ran with a Superliner train set with much more coach and sleeping car capacity (especially the later).
One would think that if this train has gained patronage by being extended to NYC, it would have at least had another Amfleet II coach car added and perhaps another Viewliner (which constantly sells out as it is). Otherwise, it has a fixed capacity and less caoacity than what it had when operating as a Superliner train set originating in Washington DC. And before it was converted back to a single level train set, Amtrak finally did align a [Northeast] Regional train to connect with the Superliner Cardinal at Washington DC.
Amtrak toyed with the idea of converting this train back to a Superliner train set, most importantly a train set that includes a Sightseer Lounge car, to try and draw a tourist crowd along its scenic route. But it would indeed originate/terminate in Washington DC. They toyed with this idea because they went back in time and saw that it supposedly had miscalculated the Cardinal's "growth" when extended to NYC, and if returned to a Washington terminus, how could it make sure patronage was maintained.
Now this differs from the daily Silver Meteor, for example, that operates with 4 Amfleet II coaches, three Viewliners, diner, Amfleet II lounge etc. If this train was truncated at Washington DC, then this consist may suffer in trying to fill it from just Washington DC south, and hoping for that connecting Regional train to/from NYC. That notion I agree would be a bad idea.
The Cardinal is partially filling the void of the Three Rivers (3x per week only) along the NEC from Newark to Philly for those that want a direct connection to Chicago - but although direct, it's a long route with not many amenities.
Yes, Amtrak needs the Three Rivers or a re-launched Broadway Limited - largely to redeem the Lake Shore Limited that has gone downhill as of late. As a separate train, it could be a separate "clean-up train" and allow the Lake Shore Limited return to a better eastbound schedule. Even if a separate "Three Rivers" if you will was combined with the Capitol Limited at Pittsburgh, continuing on to Chicago/NYC, this would (1) build back ridership lost in this market, (2) offer a a much needed second frequency between Harrisburg and Pittsburgh and (3) allow through cars to/from Chicago at Pittsburgh.
If Amtrak wanted to put sleeping class car service back in place on the NEC, I believe it could. The numbers prove they have enough Viewliners IF they wanted to restore such a service, but Amtrak has chose note to, for whatever reason. That's almost a separate issue.