With debate in Washington focused on the taxes paid by the wealthiest Americans, new data from the Internal Revenue Service shows that the effective tax rates for America’s top earners fell even lower in 2010.

The average effective tax rate fell for all income groups above $500,000, continuing a drop that has occurred for years. For incomes above $10 million, the average rate fell from 22.4 percent in 2009 to 20.7 percent in 2010. The reason for the continual drop is clear: the 2003 high-income Bush tax cuts lowered the rate on investment income, and wealthy Americans are deriving more income from investments than they ever have, the Wall Street Journal reports:

The reason for the drop in average tax rates is no secret: It’s the special 15% top rates for capital gains and dividends that President George W. Bush pushed through. In 2009, taxpayers with incomes exceeding $10 million reported 35.8% of their income as capital gains and dividends. That rose to 48.5% for 2010.

Low capital gains rates have helped the wealthy pay lower and lower tax rates even as their incomes have skyrocketed. And while capital gains income makes up almost half of the incomes of the wealthiest Americans, it accounts for 2.2 percent or less for earners under $200,000. Half of all capital gains income goes to just to the richest 0.1 percent of Americans.

The capital gains rate has been steadily eroded since President Ronald Reagan taxed such income equal to wages in the 1980s, and the result has been rising income inequality. A January 2012 study found that low capital gains rates were the biggest driver of American income inequality, which now rivals the levels seen in countries like Ivory Coast and Pakistan. In 2010, the capital gains preference helped the richest 1 percent capture 93 percent of all income gains.

Less than a week after Georgia Sen. Saxby Chambliss (R) signaled a willingness to abandon the radical anti-tax pledge authored by Grover Norquist that has brought previous debt negotiations to a standstill, another prominent Republican has joined him.

Asked last week if Norquist would hold his support for new revenues against him, Chambliss said, “I don’t worry about that because I care too much about my country. I care a lot more about it than I do Grover Norquist.” South Carolina Sen. Lindsay Graham (R) seemed to echo that sentiment today, saying on ABC’s This Week that he could conceivably abandon the pledge as part of a deal to avoid going over the so-called “fiscal cliff,” the package of spending cuts and tax increases set to take effect at the end of the year:

GEORGE STEPHONOPOLOUS (HOST): In the end, Norquist said that you’re not going to go through with this promise to raise revenues, because, quote, you like being a senator, your response?

GRAHAM: I love being a senator and i want to be a senator that matters for the state of South Carolina and the country. When you’re $16 trillion in debt, the only pledge we should be making to each other is to avoid becoming Greece, and Republicans should put revenue on the table. We’re this far in debt. We don’t generate enough revenue. Capping deductions will help generate revenues. Raising tax rates will hurt job creation. I agree with Grover that we shouldn’t raise rates, but I think Grover is wrong when it comes to we can’t cap deductions. [...] I will violate the pledge, long story short for the good of the country, only if Democrats will do entitlement reforms.

Norquist is clinging to the support he does have, even as the pledge wreaked havoc on the GOP’s candidates in the November elections. Sixteen Republican incumbent Republicans and one incumbent senator who signed the pledge lost re-election, and a total of 56 House members or candidates and 24 senators or candidates lost. As a result, a growing number are abandoning the pledge.

Still, Graham’s insistence on entitlement reforms ignores that Democrats have already made significant changes to Medicare (as part of the Affordable Care Act) and have proposed reforms to Social Security, even though the program is not in need of an immediate fix. And his claims that raising tax rates will kill jobs is tenuous, if oft-used. Reports from the Congressional Research Service and the Congressional Budget Office, both non-partisan agencies, have shown that allowing the expiration of the high-income Bush tax cuts would have little impact on economic growth.