Americans needed to be patient before deciding what effect President Donald Trump's tax cuts have had on the economy. It takes a while for companies to make investment decisions, more time for those decisions to be implemented and even more time for the resulting changes in labor demand to bid up workers' wages. It therefore takes months or even years before the full impact of the tax bill will be known. 

But it's also important to evaluate policies like Trump's tax reform as quickly as possible. Not only is this critical for deciding whether to change course, but as more time goes on, the effects of a policy can become harder to assess. Two years from now, plenty of other things will have had time to affect the economy, including Trump's trade war and natural economic forces. 

Now that the tax cut has been in effect for a half-year, the results are starting to trickle in.

First, the tax reform hasn't yet resulted in appreciably higher wages for American workers. Real average hourly compensation actually fell in the first quarter after the tax reform was passed: Official data for the second quarter isn't available yet, but private data isn't looking encouraging. PayScale's index of real wages shows a dramatic deterioration in the period: But perhaps two quarters is too early to expect results in this area.

A better gauge might be business investment − if the tax reform is spurring businesses to increase capital expenditure, as it was supposed to do, then wage increases will probably follow in due course.

Some have expressed dismay that stock buybacks seem to have taken precedence over boosting capital investment. Since the tax cuts passed, companies have been using buybacks to return record amounts of cash to shareholders − more than $700 billion in the first two quarters. That naturally raises the possibility that companies don't have good projects to invest in. If companies pass their tax windfall on to shareholders, those investors can choose to react by increasing consumption − meaning more of society's resources go to the wealthy. They can also choose to invest the money in other companies with better growth prospects − but if those companies are also reacting by returning the money to their shareholders, rather than making capital expenditures, not much is getting accomplished.

So is any of the tax-cut windfall being used to finance the capital expenditure that the economy needs? Private nonresidential fixed investment did increase as a share of the economy in the first two quarters since the reform was passed: But the level still remains below the high set back in 2015.

In summary, huge gains for wealthy shareholders combined with tepid increases in business investment and decreases in real wages don't paint a flattering picture of the tax cut's impact so far. 

There is, however, a possibility that the tax cut has acted as a Keynesian fiscal stimulus, helping to push down unemployment. Unfortunately, almost all economists now recognize that even with job growth, income tax cuts don't  stimulate the economy enough to reduce deficits, as supply-siders thought they would back in the 1980s.

Economists still held out some hope that lowering the corporate tax, which is believed to be more harmful than the personal income tax, would have a more salutary effect on the budget. Unfortunately, that hope appears to be fading, as fiscal deficits increase rapidly.

Taken together, the early results point to the possibility that tax cuts have run their course as an economic policy. The tax cuts by President George W. Bush were followed by years of underwhelming growth, implying that income taxes were not doing much damage to economic efficiency.

Reducing corporate taxes were really the last hope for the tax-cutting strategy. If even that doesn't provide more than a small momentary fiscal stimulus, then we've reached the end of the usefulness of the tax-cutting approach to economic policy.

Noah Smith is a Bloomberg Opinion columnist. He was an assistant professor of finance at Stony Brook University, and he blogs at Noahpinion.