The GND is impossible.
1, we don't have enough money to make it feasible.
2, there is not enough manpower in the construction fields to make it happen (that number keeps dropping, as more people want art history degrees).
Can we make strides? Absolutely. I know this, because already have.
Option #2 is a significantly bigger hurdle than #1. That and having enough steel/concrete/resources is the stuff that actually matters for ambitious gov't programs. And labor can be corrected by reincentivizing trade school paths and "up-incentivizing" engineering.
Why is #1 less concerning? Mostly because the national debt isn't like civilian debt. When the US runs a deficit of $5, that means its citizens/corporations and infrastructure received a surplus of $5. They always balance. And though the Treasury has to be attentive to the balance, deficits and debt are not automatically "bad" unless it results in consequences like default or inflation.
First, let's get ahead of the first: Default ain't happening. Full stop. Politicians may claim there's a risk of "national bankrupcy" but that's true nonsense - just fear mongering to win. Second up: inflation can happen. It's the thing to watch like a hawk. But inflation pains are not likely in this environment. Just look at inflation changes since 2000. That's the last year we had a national budget surplus and it's the year when national debt was its lowest across many of our lives.
We've soared by trillions in debt since, and inflation hasn't been a bogeyman of ours. At least not yet. Because we appropriately adjust our interest rates and the Treasury has a very strong bond market to account for every deficit. And that's ignoring how our national assets (nearing $120
trillion) have climbed faster than our debts during these same years.
All of which are good arguments for taking on MORE debt than we have during good economic stretches. Because taking less debt is missing opportunities to strengthen our infrastructure and private sectors without real consequences. It's also a good argument that the average person misunderstands/overemphasizes national debts and deficits. Inflation signals are the ones to pay attention to - not bankrupcy or "how will we ever pay China?" fear mongering.
Anyway, this isn't to say that the full GND as popularized so far can be paid for by taking on more debt. But we could definitely afford an intermediate version. We just need to find one (trivial), agree on it (impossible for now), and remember that US history already has a famous example of taking on New Deal debt to solve massive problems.