This chart has something for both Democrats and Republicans. It’s federal personal income taxes as a share of personal income (four quarter moving average).
If I was a Republican economist, I would point out that federal income tax revenues at the end of the 1990s rose to very high levels, in excess of 12% of personal income. That’s historically a signal for tax cuts.
If I was a Republican economist, I would also point out that tax revenues have bounced back since the Bush tax cuts. Federal personal income taxes were 9.9.% of personal income in the four quarters ending with 2007III. The average since 1960? 10%.
If I was a Democratic economist, I would point out that the Bush tax cuts drove federal income tax revenues to very low levels historically, just over 8% of personal income.
If I was a Democratic economist, I would also point out that if the economy is going into a slowdown, then we would expect tax revenues to fall, so this 10% may be the peak of the cycle.
Final note: If we average the past ten years, we get 10.1%. I think I see a pattern here.