Republican White House hopeful Mitt Romney drew fierce Democratic fire over his tax bill, part of a plan to paint the multi-millionaire as out of touch with middle America. The former Massachusetts governor, who could seal up his party\'s nomination with a convincing win in South Carolina\'s primary on Saturday, bowed to mounting political pressure and said he would release his 2011 tax filings come April. And Romney, thought to be worth between $190-$250 million, said he pays an effective tax rate of about 15 percent, which would be in line with tax laws that President Barack Obama has denounced as lopsidedly favoring the rich. \"What\'s the effective rate I\'ve been paying? It\'s probably closer to the 15 percent rate than anything,\" the Republican, who touts his business acumen as his top asset, told reporters after a rally in Florence, South Carolina. Romney noted that his rate is lower than the highest tax bracket on wage income, 35 percent, because his money \"comes overwhelmingly from investments made in the past\" and benefits from a tax code meant to encourage investments. In a rare campaign-related salvo from the White House, spokesman Jay Carney said Romney\'s disclosure \"illuminates\" an ongoing debate about widening US income inequality and that Obama thinks the rich must \"pay their fair share.\" Obama, whose 2010 returns showed he paid an effective tax rate of 26 percent, \"believes that we ought to change the law\" so that \"everybody... gets a fair shot at the American dream,\" Carney told reporters. Carney stopped short of calling on Romney to publish his tax returns, but pointed out that leading past candidates, including then-senator Obama, had revealed their personal financial records -- and not just one year\'s worth. Carney also noted that George W. Bush, Bill Clinton and nominees for each party for years had provided the information and suggested Romney\'s own father George Romney established the tradition in the 1968 presidential campaign. In Florence, South Carolina, Mitt Romney acknowledged that \"people will want to see\" his tax filings, in keeping with that tradition, and said \"we\'ll wait until the tax returns for the recent year are completed, and then release them.\" \"I got a little bit of income from my book, but I gave that all away. And then I get speaker\'s fees from time to time, but not very much,\" said Romney, who has a wide lead over his rivals here in recent public opinion polls. The Democratic National Committee, the White House\'s political arm, noted in a statement that Romney\'s financial disclosure forms showed he made about $375,000 from nine speeches given between February 2010 and February 2011. And the DNC pointedly referred to a US Census finding that the median US annual income was $50,046 -- slightly more than Romney\'s average speech pay-day. The DNC accused Romney -- who has blasted Obama\'s \"bitter politics of envy\" and recently said discussions of income inequality belong \"in quiet rooms\" -- of championing the current system because \"he is benefiting.\" The Democratic onslaught reflected a political calculation: The sour US economy, with national unemployment stubbornly high three years after Obama came into office promising \"hope and change,\" could cost the Democrat another term in the November 6 elections. In recent weeks, helped by Romney\'s increasingly desperate rivals for the Republican nomination, Democrats have blasted him over his time at Bain Capital, zeroing in on the firms dismantled and workers fired by his company. Romney has shot back that four companies helped or built by Bain have created 120,000 jobs -- a calculation that omits failed firms and lost jobs in its bottom line and has been repeatedly criticized by nonpartisan fact-checking organizations. Still, the former governor\'s Republican rivals -- veteran Representative Ron Paul, former senator Rick Santorum, former House speaker Newt Gingrich, and Texas Governor Rick Perry -- are running out of time. Gingrich, speaking at a campaign event in Florence, optimistically urged Santorum and Perry to throw their lot in with him and break Romney\'s increasingly tight hold on the nomination. \"So I am respectful that Rick has every right to run as long as he feels that\'s what he should do, but from the standpoint of the conservative movement, consolidating into a Gingrich candidacy would in fact virtually guarantee a victory on Saturday,\" he said. \"And I\'d be delighted if either Perry or Santorum wanted to do that.\" Romney got a fresh boost Tuesday with a new poll showing he has pierced the important 30 percent threshold of support among Republicans nationally for the first time, and now enjoys the backing of 37 percent of those surveyed.