By MARCO RUBIO
WSJ.com

Americans have built the single greatest nation in all of human history. But America's exceptionalism was not preordained. Every generation has had to confront and solve serious challenges and, because they did, each has left the next better off. Until now.

Our generation's greatest challenge is an economy that isn't growing, alongside a national debt that is. If we fail to confront this, our children will be the first Americans ever to inherit a country worse off than the one their parents were given.

Current federal policies make it harder for job creators to start and grow businesses. Taxes on individuals are complicated and set to rise in less than two years. Corporate taxes will soon be the highest in the industrialized world. Federal agencies torment job creators with an endless string of rules and regulations.

On top of all this, we have an unsustainable national debt. Leaders of both parties have grown our government for decades by spending money we didn't have. To pay for it, they borrowed $4 billion a day, leaving us with today's $14 trillion debt. Half of that debt is held by foreign investors, mostly China. And there is no plan to stop. In fact, President Obama's latest budget request spends more than $46 trillion over the next decade. Under this plan, public debt will equal 87% of our economy in less than 10 years. This will scare away job creators and lead to higher taxes, higher interest rates and greater inflation.

Betting on America used to be a sure thing, but job creators see the warning signs that our leaders ignore. Even the world's largest bond fund, PIMCO, recently dumped its holdings of U.S. debt.

We're therefore at a defining moment in American history. In a few weeks, we will once again reach our legal limit for borrowing, the so-called debt ceiling. The president and others want to raise this limit. They say it is the mature, responsible thing to do.

In fact, it's nothing more than putting off the tough decisions until after the next election. We cannot afford to continue waiting. This may be our last chance to force Washington to tackle the central economic issue of our time.

"Raising America's debt limit is a sign of leadership failure." So said then-Sen. Obama in 2006, when he voted against raising the debt ceiling by less than $800 billion to a new limit of $8.965 trillion. As America's debt now approaches its current $14.29 trillion limit, we are witnessing leadership failure of epic proportions.

I will vote to defeat an increase in the debt limit unless it is the last one we ever authorize and is accompanied by a plan for fundamental tax reform, an overhaul of our regulatory structure, a cut to discretionary spending, a balanced-budget amendment, and reforms to save Social Security, Medicare and Medicaid.

There is still time to accomplish all this. Rep. Dave Camp has already introduced proposals to lower and simplify our tax rates, close loopholes, and make permanent low rates on capital gains and dividends. Even Mr. Obama has endorsed the idea of lowering our corporate tax rate. Sen. Rand Paul, meanwhile, has a bill that would require an up-or-down vote on "major" regulations, those that cost the economy $100 million or more. And the House has already passed a spending plan this year that lowered discretionary spending by $862 billion over 10 years.

Such reductions are important, but nondefense discretionary spending is a mere 19% of the budget. Focusing on this alone would lead to draconian cuts to essential and legitimate programs. To get our debt under control, we must reform and save our entitlement programs.

No changes should be made to Medicare and Social Security for people who are currently in the system, like my mother. But people decades away from retirement, like me, must accept that reforms are necessary if we want Social Security and Medicare to exist at all by the time we are eligible for them.

Finally, instead of simply raising the debt limit, we should reassure job creators by setting a firm statutory cap on our public debt-to-GDP ratio. A comprehensive plan would wind down our debt to sustainable levels of approximately 60% within a decade and no more than half of the economy shortly thereafter. If Congress fails to meet these debt targets, automatic across-the-board spending reductions should be triggered to close the gap. These public debt caps could go in tandem with a Constitutional balanced budget amendment.

Some say we will go into default if we don't increase the debt limit. But if we simply raise it once again, without a real plan to bring spending under control and get our economy growing, America faces the very real danger of a catastrophic economic crisis.

I know that by writing this, I am inviting political attack. When I proposed reforms to Social Security during my campaign, my opponent spent millions on attack ads designed to frighten seniors. But demagoguery is the last refuge of the spineless politician willing to do anything to win the next election.

Whether they admit it or not, everyone in Washington knows how to solve these problems. What is missing is the political will to do it. I ran for the U.S. Senate because I want my children to inherit what I inherited: the greatest nation in human history. It's not too late. The 21st century can also be the American Century. Our people are ready. Now it's time for their leaders to join them.

Mr. Rubio, a Republican, is a U.S. senator from Florida.