Interesting article at The Daily Signal covers the main points.
It appears - as always - that people's political viewpoint colours their interpretation of economics. Instead of answering the actual question, it drifts off into "How should a government respond to a recession?"
The right-wingers are supply siders, they say that the best way to stimulate the economy is tax cuts; the left-wingers are Keynesians and say that the best way to stimulate the economy is deficit spending (quite on what is not clear). Really, those are two ends of a spectrum - tax cuts (if you're not already in the wrong side of the Laffer Curve) implies deficit spending just as much as, er, deficit spending. Unless core government spending is reduced during a recession, which most would agree is a bad idea. The Tories talk a good game on austerity, but they are actually running massive deficits in supposedly better times, which even Keynes said was a bad idea.
In normal times, of course supply creates demand. Not necessarily for the product itself but for other things. With electricity, there is a nice feed back loop. Electricity was just something scientists stumbled across in the lab; having discovered it, people worked out what it could be used for (electric lighting and radios). So we have demand for light bulbs and radios. The more light bulbs and radios people use, the more electricity is produced and the more the National Grid is extended etc. Meaning that more people can buy light bulbs and radios, etc.
As to the proposed government responses to recessions, both are wrong, as they don't address why we have recessions in the first place. The reason is that when the land-price/credit bubble pops after eighteen or so years, banks try and claw back as much of their loans as possible. They can't speed up the rate at which people can pay off mortgages on land, so they call in loans from - and reduce lending to - the productive economy instead (be that loans to businesses or consumer credit loans). That has knock-on effects which no amount of tax cuts or deficit spending can prevent.