Similarly, what about a cap on the state and local tax deduction? Initial conservative reaction will likely be hostile: Why increase some people's federal tax bills? Isn't that attacking a core Republican constituency?
Actually, it's not and not. The state and local tax deduction is worth a lot more to high earners than to modest earners, and it's worth nothing to the nearly half of households that don't pay federal income tax.
But it's worth the most to high earners in high-tax, high-spending states. Those people are more likely to be Democrats than Republicans. The 2008 exit poll tells the story.
Nationally, voters with incomes over $100,000 voted 49 percent to 49 percent in the presidential race. Those with incomes over $200,000 voted 52 percent to 46 percent for Barack Obama.
In high-tax, high-spending states, Obama did even better with high earners. He carried $100,000-plus voters with 55 percent in Connecticut, 56 percent in New York, 52 percent in New Jersey, 55 percent in Maryland, 54 percent in Illinois and 57 percent in California.
All those states have high state income taxes except for Illinois, and it increased its income tax rate by two-thirds earlier this year. And those states contain a huge share of the nation's highest-priced housing.
In contrast, in low-tax, low-spending states with relatively inexpensive housing, $100,000-plus voters favored John McCain, who won 65 percent of their votes in Texas, 55 percent in Florida and 61 percent in Georgia.
It is no coincidence that the high-tax, high-spending states tend to have strong public employee unions. In effect, the unlimited state and local tax deduction is a federal subsidy of the indefensibly high pay, benefits and pensions of public employee union members. Limiting the state and local tax deduction would create a political incentive to hold those costs down.
So ironically, limiting high earners' lucrative tax deductions may prove a harder sell among Democrats than Republicans. But maybe Republicans should give it a try anyway.