How high should taxes be? High enough to cover expected outlays going forward — but no higher.
That’s because any additional revenue would be used to pay down the federal debt, which is a bad idea. It was almost surely a mistake to run up this much debt in the first place, but now that we’ve got it, the best thing to do is to keep it forever.
Every $100 in outstanding debt commits the government to making payments with a present value of $100, and hence to collecting tax revenues with a present value of $100. In a world where the interest rate is 3%, the options include collecting (and paying off) $100 immediately, or $50 this year and $51.50 next year, or $11.38 a year for ten years running, or $3 a year forever. Because deadweight loss (i.e. the economic damage due to the disincentive effects of taxes) is roughly proportional to the square of the tax rate, it turns out that the latter — the policy of paying interest forever without ever making a principal payment — is (at least roughly) the policy that minimizes the present value of deadweight loss.
(For those checking this at home, use the fact that tax revenue looks roughly like At-Bt2 where t is the tax rate.)
In other words, as far as the existing debt goes, we’re hosed no matter what we do — it’s painful to pay it off, and painful to keep paying interest forever. But at least if we pay interest forever, we’re minimizing the deadweight losses associated with raising taxes.
The right policy, then, is to estimate future outlays including interest on the existing debt but not including any principal payments on that debt, and to set tax rates so that revenues match those outlays in a typical year. Insofar as Mr. Obama asks for more than that, he’s either a) planning higher future spending than he’s admitting to or b) embarking on a reckless policy of debt reduction.
Note: The above assumes that spending policies and tax policies can be set separately (subject to the constraint that tax revenues are at least high enough to cover interest payments). Things of course get more complicated if you believe that debt levels and/or tax rates constrain future spending through some political mechanism. I’ve often heard this alleged, but I’m unaware of any strong evidence for this assertion.