In the heat of a presidential election campaign in the United States, contentious questions are emerging about the fairness of the country's taxation system and the growing income and wealth gap between the richest Americans and the vast masses of their countrymen.

The issue of tax fairness and wealth in America came to the fore this week in the person of Mitt Romney. He is a one-time venture capitalist and former governor of Massachusetts. He also is the leading Republican contender to oppose President Barack Obama, a Democrat, in the national presidential election next November. Romney has disclosed that his personal fortune is between $190 million and $250 million, making him one of the wealthiest men to run for the U.S. presidency in modern times.

But it was his revelation that he has paid a federal tax rate of about 15 percent on his vast income in recent years — compared with other taxpayers obligated to pay as much as 35 percent — that has set off a new debate about the fairness of the country's tax code. In addition, Romney characterized as “not very much” the more than $374,000 he earned last year in speaking fees, a figure that by itself lands him among the top 1 percent of the country's earners.

Larry Sabato, a long-time political analyst at the University of Virginia, says tax fairness and income inequality are likely to play a role in the election because of years of slow economic growth in the U.S.

Romney says that in the past decade, most of his income has come from his investments, which in the U.S. are taxed at a top rate of 15 percent. By comparison, U.S. workers who make most of their income from salaried jobs are taxed at progressively higher rates, with the 35 percent figure assessed on income above $379,151. About half of the country's households pay no income taxes, although many still pay payroll taxes to cover their contributions to the government's pension and health care plans for older Americans.

Tax issues are certain to play a key role in the national presidential election, whether Romney or one of his rivals wins the Republican Party nomination.

Mr. Obama has called for higher taxes on the country's wealthiest taxpayers, but Republican lawmakers in Congress have steadfastly rebuffed his efforts. They say higher taxes on the wealthy would inhibit job growth at a time the country can ill afford it.

U.S. presidential candidates have traditionally released their federal tax returns, as Mr. Obama has for several years. He and his wife Michelle reported $1.8 million income in 2010 and have paid more than 25 percent of that in federal taxes. Under pressure from other Republican presidential contenders and Mr. Obama's supporters, Romney has reluctantly agreed to release his 2011 tax return when he files it in April.

Whether Romney's wealth and his effective tax rate compared to Mr. Obama's resonates with the voting public is open to question. Political analyst Sabato does not think it will be the deciding factor. That's because, he says, voters will be more swayed by the state of the overall economy.

Wealthy elites have always had a prominent place in American society. But now, as the U.S. struggles to regain its economic footing after its worst recession in seven decades, the disparity has widened between the most prosperous and the country's middle class, as well as its poorest residents. About 13 million Americans remain unemployed, even as the U.S. jobless rate has declined to its current 8.5 percent level. Millions of families have lost their homes to bank takeovers because they could no longer make monthly loan payments.

The Economic Policy Institute in Washington said in an analysis of American workers' wealth that in 2009 the richest 1 percent of U.S. households had a net worth that was 225 times greater than the median household's net worth – the greatest disparity on record.

Part of that disparity has been fueled by the cuts in the tax rates on investments and stock dividends, which over the past two decades have benefited the wealthy – who own the most stocks. There was a 28 percent tax rate on such investments in 1986, the same as for ordinary income, but it has been trimmed steadily since then to the current 15 percent figure.

Sabato says that Americans often view wealth in different ways, depending on their own fortunes at the moment – and in good times are more tolerant of income gaps.

With many Americans struggling to pay their bills, and the possibility of two wealthy candidates in a head-to-head matchup for a four-year term in the White House, the debate over the role of wealth in the U.S. is unlikely to disappear.