What does trickle down economics mean in real terms?

I realized I didn't answer your questions in the top comment u/Total_Candidate_552. So one by one:

So when congress cuts taxes, what can Americans expect?

The quintessential model used to answer this question is called the "Laffer curve." You can think about it as a graph -- on the Y axis is tax revenue and on the X axis is the tax rate. The theory holds that the relationship between these two variables is shaped like an upside down U -- meaning at low tax rates there is low revenue and as you increase tax rates revenue increases, but as you increase taxes after some tax rate (the "optimal tax rate") revenue begins to decline. The reason for the decline in tax revenue after the optimal tax rate is that taxes stifle growth and there is less of a tax base to levy from. I think most economists would agree that some relationship like this does exist in the real world but that right-of-center governments propose tax rates lower than the optimal tax rate.

What kind of goods/services are affected by tax cuts?

It depends on the tax cuts. There are many kinds of taxes, such as taxes on output, taxes on transactions, taxes on property, taxes on income, etc. So it really depends on the tax being discussed. If you mean the standard Republican tax proposals, they tend to benefit the top end of town through reduced tax obligations on their income. The "billionaire taxes" or "wealth taxes" being thrown around now by the Democrats would do the opposite.

More importantly, how does the actual accounting of a tax cut work, and how many transactions do we need before an American realizes the benefits of trickle-down?

The "optimal tax rate" concept captured by the Laffer Curve answers this question. At the optimal tax rate governments do not leave revenue on the table (which implies the maximum amount of transfers from the top to everyone else through programs such as single payer health insurance or unemployment insurance) and that growth is not hindered (meaning low unemployment and high income growth). This idea relies on the assumptions that governments actually spends the revenues appropriately, and that growth actually results in low unemployment and high income growth -- both questionable.

/r/PoliticalDiscussion Thread Parent