'The Growth Fairy Model'

Kevin Williamson at the National Review Online tells Republican candidates to get real:

The Thing about Tax Cut, by Kevin D. Williamson: Every Republican tax-reform plan should be rooted in this reality: If you are going to have federal spending that is 21 percent of GDP, then you can have a.) taxes that are 21 percent of GDP; b.) deficits. There is no c.

If, on the other hand, you have a credible program for reducing spending to 17 or 18 percent of GDP, which is where taxes have been coming in, please do share it.

The problem with the Growth Fairy model of balancing budgets is that while economic growth would certainly reduce federal spending as a share of GDP if spending were kept constant, there is zero evidence that the government of these United States has the will or the inclination to enact serious spending controls when times are good (Uncork the champagne!) or when times are bad (Wicked austerity! We must have stimulus!). So even if we buy Jeb Bush’s happy talk about growth, or Donald Trump’s, the idea that spending is just going to magically sit there, inert, while the economy zips forward and the tax coffers fill up, is delusional.

There are no tax cuts when the government is running deficits, only tax deferrals.

Remembering that the "math simply does not add up" for Republicans -- partly that's Williamson's point -- let's take a look at the evidence on government spending as a share of potential GDP. This is from Paul Krugman in 2013, but the underlying trends do not change. He explains why this is the best measure to use when looking at this question:

The Non-Surge in Government Spending: The fiscal debate in Washington is dominated by things everyone knows that happen not to be true. One of those things is the notion that we have a fiscal crisis... The crucial thing to understand here is that you do need to take the state of the business cycle into account; it’s not enough simply to do what Nate Silver, for example, does, and look at spending as a share of GDP — a calculation that can be deeply misleading in the aftermath of a severe recession followed by a slow recovery.

Why does this matter? First, if the economy is depressed — if GDP is low relative to potential — the share of spending in GDP will correspondingly look high. ...

Second, there are some programs — unemployment benefits, food stamps, to some extent Medicaid — that tend to spend more when the economy is depressed and more people are in distress. And rightly so! You don’t want to take a temporary spike in UI payments after a deep slump as a sign of runaway spending.

So how can we get a better picture? First, express spending as a share of potential rather than actual GDP; we can use the CBO estimates of potential for that purpose. Second, keep your eye on the business cycle — and, in particular, on how spending is evolving now that a gradual recovery is underway.

So, let’s look first at a longish time series of total government spending as a share of potential GDP:

Ratio of government spending to potential GDP

What you see is not a sustained upward trend: there’s actually a considerable fall during the Clinton years, reflecting in part falling defense spending, then a more modest rise in the Bush years, mainly reflecting spending on the War on Terror (TM), and finally a temporary surge associated with the financial crisis — but much of that surge has already been reversed.

Here’s a closeup on Bush’s last two years and Obama’s first four:

That was the spending surge that was. ...

The claim is that "the idea that spending is just going to magically sit there, inert, while the economy zips forward and the tax coffers fill up, is delusional." Here's an updated graph using the latest data:

Taking away the surge from the crisis, which has been reversed, the trend in the last few decades looks pretty flat to me. To the extent that there is a tendency for the ratio to move upward in recent years, it's hardly the fault of Democrats. There is something delusional here, but it's not that spending as a share of potential GDP -- the right way to look at this question -- always rises when times are good or bad, or that Democratic administrations cannot keep spending under control.