On April 15 -- Tax Day -- we passed a landmark in the life of our republic. Almost half of U.S. households -- 47 percent, a record number -- paid no federal income tax for 2009, according to the Tax Policy Center in Washington, D.C. Either their incomes were too low or they qualified for enough deductions, credits and exemptions to wipe out their tax liability.

We hear continually that better-off Americans should pay their "fair share" of taxes. For President Obama and his allies in Congress, it's an article of faith that they don't. You'd never guess, from the clamor, that the top 1 percent of income earners pay a whopping 40 percent of all federal income taxes. (Yes, you read that right.) The top 5 percent pony up 60 percent, while the top 10 percent contribute more than 70 percent. The bottom 50 percent pay only 3 percent of total income tax revenues.

In 2009, we reached a point where almost half of American families did not contribute to the costs of our national defense, our federal welfare programs or our massive new hobby of federal bail-outs. (In 1990, in contrast, only 21 percent of families were nonpayers.) As federal spending soars and our country's mind-numbing deficit mounts, fewer and fewer of us are footing the bill.

The United States is becoming a nation where a swelling group of citizens -- not poor, but middle class -- is benefiting from government largesse wholly underwritten by another group. And here's a new wrinkle: Most families that don't pay federal income taxes will actually get a cash payment from Uncle Sam, courtesy of the tax code. The reason? A burgeoning number of refundable tax credits, which can eliminate all of a filer's income tax liability and then entitle him or her to a check for any value of the credit that remains.

In 2010, the three largest refundable credits -- including the earned income tax credit and the Making Work Pay credit, "will redistribute over $114 billion to the families that claim them," according to the Heritage Foundation's Curtis Dubay.

President Obama calls this "spreading the wealth around."

It's true that Americans who don't pay income tax do pay other kinds of federal taxes -- notably payroll taxes for Social Security and Medicare and gasoline and cigarette taxes. Nevertheless, true dependence on government is on the horizon for an increasing number of Americans. In 2004, the bottom 20 percent of U.S. households as a group received about 75 percent of their income from the government, according to a 2007 study by the nonpartisan Tax Foundation.

A more recent Tax Foundation study found that fully 60 percent of Americans are now consuming more in government benefits and services than they contribute in taxes. Under President Obama's tax and spending policies, the figure will rise to 70 percent, according to the study.

"Look at it this way," Rep. Paul Ryan of Wisconsin has written. "Three out of 10 American families are supporting themselves plus -- through government -- supplying or supplementing the incomes of seven other households. ... This is individually unfair, politically inequitable and economically dangerous."

In 2012, the United States may hold its first federal election in which 51 percent of earners will pay no federal income taxes. These folks will have the power to vote themselves ever heftier benefits in housing, education and health care -- and send the bill to the chumps in the other 49 percent.

As we approach this tipping point, what are the implications for our democracy?

Today, amid Washington, D.C.'s heady dreams of reinventing America as a European-style welfare state, it's easy to forget the unspoken contract that has always undergirded our government "of the people, by the people, for the people."

Here's the bottom line: A democracy needs a certain sort of citizen. It needs citizens who believe they have a stake in a common political enterprise, and who take responsibility for their own lives and well-being. Such citizens know that liberty and opportunity have a price, and they expect to sacrifice -- to do their part -- to preserve this priceless birthright.

But when a majority of citizens no longer have a personal, financial stake in the nation's public policies, they have no need to weigh burdens and benefits. Democracy threatens to decay into the tyranny of the majority that our founders feared and tried to protect us against.

In his 1961 inaugural address, President John F. Kennedy issued a ringing challenge: "Ask not what your country can do for you. Ask what you can do for your country." In our day, an increasing number of Americans might be excused for having no idea what Kennedy was talking about.

Katherine Kersten is a Twin Cities writer and speaker. Reach her at kakersten@gmail.com.