Washington, DC (USA Today) -- Former Pennsylvania senator Rick Santorum released four years of tax returns Wednesday night, the most for any Republican presidential candidate this year.
The returns for 2007-10 show the income for Santorum and his wife, Karen, has grown since he left the Senate after being defeated in 2006.
The Santorums' tax returns were first reported by Politico.
USA TODAY calculated that the Santorums have paid effective tax rates between 25.4% (in 2007) and 28.5% (in 2010). That's far more than what Mitt Romney's effective tax rate was in 2010, but lower than Newt Gingrich's rate the same year.
The Santorums, filing jointly, had adjusted gross income of $659,637 in 2007.
That went up to $945,100 in 2008, about $1.1 million in 2009 and $923,411 for 2010.
The documents show Santorum earned the bulk of his income by consulting and doing public speaking for Excelsior LLC. His financial-disclosure forms show he has also earned income as a political pundit and member of corporate boards.
Tax returns became an issue in the GOP campaign when Romney declined to release his immediately. The multimillionaire did release his 2010 return and an estimate for 2011.
Romney's documents showed he paid an effective tax rate of 13.9% on adjusted gross income of $21.7 million in 2010.
Much of Romney's income comes from capital gains and dividends, which are taxed at 15% and not the top rate of 35% for wages and ordinary income.
--Update at 9:45am--
Rick Santorum used his tax returns to make contrasts with Mitt Romney, saying in interviews last night that he doesn't have the dividend income of his rival and had to use his earnings to pay down his mortgage.
In an interview on CNN Wednesday night, Santorum noted that two of his seven children are in college, his youngest daughter has a genetic disorder requiring care, and he has a house that lost value in the economic downturn.
"I took a lot of that money and actually paid down a rather significant mortgage to the point where ... my mortgage was still below the value of my house," Santorum said. "We've had some expenses and we've been very blessed to have the opportunity to be able to handle those and still be ... in the black."
Santorum often stresses his blue-collar roots, frequently bringing up his coal-miner and immigrant grandfather as an example of his upbringing.
He told CNN last night that he was "very successful" in making money -- sometimes taking six or seven jobs doing consulting work or traveling to make paid speeches.
Santorum also said he was "very successful" in paying his taxes, and estimates his house in the Virginia suburbs of Washington, D.C., lost about 40% of its value.
Romney, a former Massachusetts governor, is a multimillionaire and one of the wealthiest presidential candidates in recent years. His 2010 tax return showed he had about $21.7 million in income, primarily from investments, and paid about $3 million to the Internal Revenue Service.
"He had dividend income," Santorum told ABC News on Wednesday night. "He had capital gains income which is taxed at 15%. I had ordinary income which got taxed at a higher rate."
The highest tax rate for ordinary income -- such as wages and salaries -- is 35%.