Well, you're not missing something in the fact that it's BS. The concept of trickle down economics is that the rich will take that extra tax money and create jobs with said money. The reality is they just use that money to bribe their way into more money via lobbying for tax breaks, etc.
I'm reminded of the Dave Chapelle sketch where the US gov't gives all the black people in the country reparations money. They then go out and spend it all on cars, cloths, electronics, etc which stimulates the economy. A hilarious, over simplified, and racist sketch but still some major truth is in there none the less. If the republicrates wanted to stimulate the economy they would help the poorest people financially.