The national debt clock is spinning faster every year.

At last check, it was approaching $16.4 trillion. Just four years ago, it was $10.6 trillion.

The skyrocketing number is, to say the least, reason for concern for every American.

Here's why:

As of today, every household in the United States owes about $140,000 of this debt.

More On This... The Cost of Spending: Federal government racking up huge tab

The country is borrowing roughly $6 billion every day, and $239 million every hour. Put another way, that's $4 million every minute.

The country runs up so much debt for a fairly basic reason -- it spends far more than it takes in. This year, for every dollar in revenue the federal government brought in, it spent two dollars and six cents. That shortfall over the course of the year adds up to the annual deficit. The national debt -- or total accumulated debt -- is the sum of all annual deficits, minus any surpluses.

Politicians talk about deficits and the debt all the time. But how to get politicians to come to some agreement to get the debt clock to slow down, or even tick back the other way, continues to be a challenge.

It might help to look at the arc of the national debt over the decades.

Throughout U.S. history, while the amount America owes has ebbed and flowed, our habit of spending more than we take in is nothing new.

While the U.S. is currently at the highest level of debt ever, 1835 saw the lowest-recorded debt at just $34,000 under President Andrew Jackson. There was an unsuccessful assassination attempt on him that year.

In 1865, a president who was killed in an assassination attempt, Abraham Lincoln, oversaw a debt of $3 billion.

The numbers would eventually grow.

Fast forward to "Black Tuesday" in 1929, the most devastating stock market crash in U.S. history, and the national debt rose to $17 billion.

Then came World War II, and by D-Day in 1945, the debt had ballooned to $259 billion.

Following the 2008 financial crisis -- which is often referred to as the start of the worst financial crisis since the Great Depression -- the debt crossed the $10 trillion mark.

And it continues to rise, well past $16 trillion today.

Economist Robert Genetski, author of the book "Classical Economic Principles & the Wealth of Nations," believes history shows that when government spending increases much faster than spending in the overall economy, the private sector and economy overall suffers.

"(From) 1945-1947, there was a huge cut in government spending because of the winding down from WWII, and the people who thought government spending was holding the economy up were all predicting a major depression at that time," he said.

"What happened was for the first time in 15-16 years there was a huge increase in private spending on goods and services per person ... and that was the real recovery. The recovery wasn't World War II when we were fighting for our survival and spending money to ensure that survival, the real recovery came after World War II."

Bill Clinton's budget director Alice Rivlin noted the challenge in curbing spending.

"Many people rail about the government does too much -- on the other hand, as soon we have a serious storm they are saying the government hasn't done enough. So you have to be very specific about this," she said. "The driving force for additional government spending is not discretionary spending. It's this coming tsunami of older people that we have to cope with and, yes, we expect Medicare spending to grow. And the question is does it have to grow that fast, and I don't think it does."

John Taylor, a Stanford University economist, said because of the interest on the debt, time is running out to deal with the problem.

"There's lots of people that will lend to us so far as long as our debt doesn't get so large they become suspicious that we'll pay it back," he said. "If we don't correct this problem, interest will tend to dominate our whole spending -- it'll be greater than defense or Social Security.

"We have history to guide us. When debt gets too high, people are skeptical about lending, then you run into a crisis like we've seen in Greece and many other countries. So it's dangerous when it gets too high, and we are moving close to that dangerous level every day."