The program's trustees recently set the table for a potentially bruising battle on Capitol Hill when it confirmed what it has been forecasting for several years—that Social Security's Disability Insurance trust fund is expected to be depleted by the end of 2016.

As the public braces for that debate—it could foreshadow the more politically charged question of how to fund the larger retirement trust fund, which is expected to exhaust its surplus in 2034—evidence is growing that the country is more dependent on Social Security than ever.

A study by the Congressional Joint Economic Committee showed that almost one-third of Americans will rely on Social Security to provide 90 percent or more of their retirement income.

And for almost two-thirds of Americans, Social Security checks will account for the majority of retirement income.

As is, Social Security is the biggest drain on the federal budget.

In its annual long-term budget report released earlier this year, the Congressional Budget Office said 59 million beneficiaries are expected to receive $833 billion in checks in 2015, accounting for one-quarter of all federal spending.

That scenario will only get worse, said the CBO. In 2010, the program paid out more in benefits than it received in tax revenue for the first time in the program's history.

And that was before baby boomers began leaving the workforce. This year, about 25 percent of the population is 65 or older. By 2025 that number will be 33 percent, and 2040 it will be close to 40 percent.

Put in terms of total beneficiaries, the 59 million people receiving benefits this year will jump to 78 million in ten years, and 100 million in 25 years.

Those are the immovable facts. In July, the Social Security Administration released its trustees report, showing the two trust funds that make up the program—the Old Age and Survivors Insurance Fund and the Disability Insurance Trust Fund—will be depleted in 2034.

But separate the two funds and the situation officially becomes urgent. The disability trust fund, or SSDI, which was created in 1956 when President Dwight Eisenhower signed amendments to the Social Security Act into law, now supports nearly 11 million Americans, who receive a monthly check averaging a bit more than $1,100.

If Congress does not act before the end of 2016, 10.8 million Americans will see about a 20 percent reduction in their monthly checks.

About $11 billion in SSDI was paid out in July. In order to secure those benefits, President Obama has advocated borrowing from the larger retirement fund.

By law, Congress must authorize that, as Social Security's trustees are required to manage each program independently.

That funding tactic has been done 11 times previously. Treasury Secretary Jack Lew, the trustee that oversees the funds, said borrowing from the retirement fund was "a common sense solution" to shoring up the disability fund's solvency.

But in their report, the trustees also said that while borrowing the money was necessary, it was not sufficient. Congress must enact other measures to assure the long-term solvency of the disability program, they said.

If the current temperature on Capitol Hill is any indication, consensus on addressing the immediate problem of the disability fund is a long way off.

Sen. Orrin Hatch, R-Utah, Chairman of the Senate Finance Committee, expressed frustration with what he thinks is the Obama Administration's failure of leadership to advance a bipartisan effort to address the immediate issue with the disability fund.

"Sadly, we have yet to see such an effort," Hatch said in a statement after the Social Security Administration released its trustees' report.

"The President simply advocates kicking the can down the road to confront the impending disability trust fund depletion, by taking funds out of the retirement trust fund, which, itself, is headed toward depletion."

Other prominent Republicans have indicated a willingness to draw a line in the sand, even as beneficiaries of the disability trust fund are expected to start seeing cuts in benefits about when Americans go the polls to elect a new president in 2016.

In January, prominent Republicans on the Ways and Means Committee in the House of Representatives issued a rule requiring legislative action to fix the disability trust fund.

That rule is designed to prevent Congress from authorizing borrowing from the larger Old Age and Survivors fund, without addressing new funding requirements and program designs to deal with the systemic solvency issue in the trust.

Rep. Sam Johnson, R-Texas, chair of the Ways and Means Subcommittee on Social Security, said borrowing from the larger fund amounts to "raiding the Social Security retirement program to bail out the disability program."

For his part, Rep. Paul Ryan, R-Wisconsin, chair of the Ways and Means Committee, told a hearing in July that he was not going to allow the cuts to disability benefits under his watch.

"No 20 percent cut," said Ryan. "Full stop. Not gonna happen."

But exactly how those cuts will be prevented if borrowing from the larger fund is prohibited remains unclear. Ryan is part of a cohort of Republicans that thinks fraud and poor program design have pushed the disability fund underwater.

Enrollment in the program has more than doubled since 1980. An aging workforce is one explanation of that phenomenon. So is the number of workers who lost their jobs in the last recession.

But Republican critics of the program say the process for vetting applicants has been liberalized over the years.

The program's defenders counter that data from the Social Security Administration shows only 45 percent of disability applications were granted between 2001 and 2010.

Last February, Sen. Hatch and Reps. Ryan and Johnson introduced legislation in both chambers of Congress that would prevent people from receiving Social Security disability benefits and unemployment benefits at the same time. A comparable proposal in President Obama's 2016 budget estimated $2 billion in savings over 10 years from that prohibition.

Other legislation has been proposed by Hatch to address fraud in the disability determination process.

None fully address the long-term projected shortfalls in the disability insurance program, which the Social Security Administration says has $1.2 trillion in unfunded obligations over the next 75 years.

To address the extent of that shortfall, Congress is going to have to pass overarching Social Security legislation that will likely have to include increased payroll taxes, cuts to benefits, and extending the retirement age.

Meantime, Democrats in the House and Senate, including Presidential candidate Sen. Bernie Sanders, I-Vermont, are advocating for increasing Social Security benefits for certain portions of the population.