Modern LED grow lights require minimum 35 watts per square foot to grow things beyond just lettuce, which is around 1.5 million watts per acre. Americans currently consume a bit over 2.5 acres of farmland produce per year, however you could get that down to 1 acre without much problem by cutting out some of the less land efficient crops likes fruit trees, especially when talking indoor grow.

So I would expect bare minimum energy requirements to be near 1.5-2 million watts per person for 12-16 hours a day for indoor food sustainability.

This is of course not accounting for fertilizer which has large energy requirements or anything more than the most simple and basic of climate control.

And how soon would their building be turned into yet another polarizing issue, or their building farmed out to contracting companies who would make most of the money disappear?

A global response on the scale of Covid to build vertical farms would reduce the severity of the famine dramatically.

It would be expensive, but the alternative would be burning cities and food riots. I can hardly imagine the USA avoiding a civil war considering how divisive and hostile things already have gotten

You can get hydroponics going fairly quickly, the bottleneck would be the supplies and supply chain — materials to build the with