New York Times:  Romney’s Tax Plan and Economic Growth, by Bruce Bartlett:

Mitt Romney and his running mate, Paul Ryan, are quite insistent that
their tax plan is just the elixir that the economy needs to jumpstart
growth. … In principle, a change that holds revenues constant while lowering marginal tax rates – the rate on the last dollar earned – should increase growth. That is because, in economist-speak, both the income and the substitution effects are pushing in the same direction. … What Reagan did and Mr. Romney proposes is to keep taxes constant but to reduce marginal tax rates. …

[E]conomic theory is unambiguous that holding taxes constant and
reducing marginal rates will increase growth. But it is important to
understand that this effect is neither large nor instantaneous. At best,
it will raise the long-term trend rate of growth by perhaps tenths of a
percent. With compounding, the effect can eventually be large.

But
the idea that tax reform will jump-start an economy suffering from the
after-effects of a cyclical downturn is nonsense. This can be
illustrated by looking at the impact of the 1986 tax reform.

Real
gross domestic product growth was about the same after the 1986 act
took effect in 1987 as it was before, and tax reform obviously did
nothing to forestall the 1990-91 recession. Unemployment fell, but it
had been trending downward before tax reform, and the 1986 act probably
had nothing to do with it. Within a couple of years it was trending
upward again.

By the mid-1990s, it was the consensus view of
economists that the Tax Reform Act of 1986 had little, if any, impact on
growth. In an article in
the May 1995 issue of the American Economic Review, the Harvard
economist Martin Feldstein, a strong supporter of tax reform who had
served as chairman of Reagan’s Council of Economic Advisers, found large
changes in the composition of income, but the only growth effect was a
small increase in the labor supply of married women.

In a comprehensive review
of the economic effects of the 1986 tax reform act, in the June 1997
issue of the Journal of Economic Literature, Alan Auerbach of the
University of California, Berkeley, and Joel Slemrod, the University of
Michigan economist, also found that the primary impact was on the
shifting composition of income. They could find no significant growth
effects. …

Mr. Romney’s plan is not likely to be enacted in anywhere near the form
he has proposed, if only because Congress is far more polarized today
than it was in 1986, and the major political parties are much farther
apart on the goals of tax reform. Consequently, there is little reason
to think we will see tax reform any time soon, and even if Mr. Romney’s
plan is enacted as proposed the growth effect will be small to
nonexistent.

New York Times editorial, Mr. Romney Needs a Working Calculator:

To the annoyance of the Romney campaign, members of Washington’s reality-based community have a habit of popping up to point out the many deceptions in the campaign’s blue-sky promises of low taxes and instant growth. The latest is the Joint Committee on Taxation, an obscure but well-respected Congressional panel — currently evenly divided between the parties — that helps lawmakers calculate the effect of their tax plans.

The Romney campaign claims it has six studies proving it can be done,
but, on examination, none of the studies actually make that point, or
counterbalance the nonpartisan analyses that use real math. … It is increasingly clear that the Romney tax “plan” is not really a plan
at all but is instead simply a rhapsody based on old Republican themes
that something can be had for nothing. For middle-class taxpayers
without the benefit of expensive accountants, the bill always comes due a
few years later.