Seems clear that shifting some money from SocSec to preK would lead to faster econ growth.
It goes on to link to a Jon Chait post about how we could pay for pre-k by switching to chained CPI.
As a thought exercise, it's fine. But I regularly see these false choices being set up. Awhile back Yglesias was saying that liberals should support closing libraries and giving the saved money to poor people. The thing is, I actually agree with both of these points. If I was your benevolent dictator, and had a fixed pot of money to spend on liberal nice things, I'd probably redirect some money for old people to money for young people, and would reduce spending on "programs," including libraries, in favor of just transferring money to poor people.
But these are false choices. These are not deals that are on the table. There is no fixed pot of money for liberal nice things. I'm pretty sure it would be a much better investment to take the F-35 money and spend it on pre-K. Hell, it'd probably be a better "investment" from a national security view to spend less money on flying death robots and spend it on genuine humanitarian aid (I imagine the paint on all those schools is peeling about now).
It's one thing to consider these deals if they're actually on the table, but it's another thing for liberals to negotiate with an imaginary Republican party that does not exist. Sure it can be a useful thought exercise, but it's politically meaningless.