It’s certainly not cost-effective on a relative basis when compared to air travel. The Delta Shuttle runs Chicago-NY-DC every hour on the half hour for a song. Hard to compete with that on rail.
With rail you do get the benefit of landing in the middle of the city rather than an airport 30 mins from city center, but it’s still far less expensive in both time and money to fly when the trip exceeds about 4 or 5 hours.
And, indeed, high-speed rail isn't very price competitive with budget air a lot of the time either. Doesn't mean it's a bad idea; transporting a lot of people who are willing to pay a premium off the roads and out of airports may well be a net win. But understand that it's premium travel.
With rail you do get the benefit of landing in the middle of the city rather than an airport 30 mins from city center, but it’s still far less expensive in both time and money to fly when the trip exceeds about 4 or 5 hours.