• Donald Trump's tax-cut plans and other agenda items would hasten Social Security's insolvency, a nonpartisan budget group said.
• The Republican nominee's proposals would also expand Social Security's cash shortfall by trillions of dollars and lead to even steeper benefit cuts in the coming years, the group estimated.
• Both Trump and Democratic nominee Kamala Harris have vowed to "protect" Social Security and Medicare.

Former President Donald Trump's campaign plans would significantly accelerate the already-fast-approaching date when Social Security is projected to run out of money, a nonpartisan budget group said Monday.

Trump's agenda would make the popular government program, relied upon by millions of American seniors, insolvent in six years — shrinking the current timeline by a third, the group found.

The Republican nominee's proposals would also expand Social Security's cash shortfall by trillions of dollars and lead to even steeper benefit cuts in the coming years, said US Budget Watch 2024, a project of the Committee for a Responsible Federal Budget.

"We find President Trump's campaign proposals would dramatically worsen Social Security's finances," the CRFB budget group said in a blog post.

The Trump campaign pushed back fiercely on the post.

"The so-called experts at CRFB have been consistently wrong throughout the years," spokeswoman Karoline Leavitt said in a statement to CNBC.

Trump "will continue to strongly protect Social Security in his second term," Leavitt said. She claimed that Democratic nominee Kamala Harris posed the real threat to the program's solvency, arguing that her policies would usher in a flood of undocumented immigrants that would "cause Social Security to buckle and collapse."

Only certain noncitizens are eligible to qualify for Supplemental Security Income benefits.

Social Security trust funds are set to be exhausted by Fiscal Year 2034, according to the Congressional Budget Office. Fiscal years begin in October.

The Social Security trustees' projections show the program's combined funds may only be able to pay full benefits until 2035. However, the trust fund Social Security relies on to pay retirement benefits may run out even sooner, in 2033.

Both Trump and Vice President Kamala Harris, the Democratic nominee, have vowed to "protect" Social Security and the government-run health insurance program Medicare, while opposing any cuts.

At the same time, Trump has vowed to enact a growing list of tax cuts targeting key groups of Americans.

He has proposed eliminating taxes on seniors' Social Security benefits, ending taxes on service workers' tips and overtime wages, lowering the corporate tax rate even further, and imposing sweeping across-the-board tariffs, which are taxes on imported goods.

The tax-cut plans, along with Trump's pledge to carry out mass deportations as soon as he takes office, "would all widen Social Security's cash deficits," the CRFB said in Monday's post.

Specifically, the group found that his agenda would:

• Boost Social Security's 10-year shortfall by $2.3 trillion through FY 2035;
• Accelerate its insolvency timeline to FY 2031 from FY 2034;
• Cause a 33% across-the-board benefit cut in 2035 (up from the 23% cut the CBO currently projects);
• Increase its annual shortfall by about 50% in FY 2035; and
• Force an equivalent reduction of current benefits by about one third, or an increase in revenue by about one half, to restore Social Security's 75-year solvency.

Those findings are no surprise, given that Trump's plans involve cutting taxes that bring significant revenue to Social Security's trust funds, said Maria Freese, senior legislative representative at the National Committee to Preserve Social Security and Medicare.

"If you cut income taxes and cut payroll taxes, then you're going to have an impact on Social Security," Freese said.

"Depending on the proposal that you're looking at, it could have a dramatic impact over time, and particularly when you're looking at a trust fund depletion date that's within the decade anyway," she said.

The National Committee to Preserve Social Security and Medicare has endorsed Harris for president.

"I don't believe the Trump campaign is looking to undermine Social Security," said Andrew Biggs, senior fellow at the American Enterprise Institute and former principal deputy commissioner of the Social Security Administration. "I just don't believe it's front of mind for them as they put out various proposals."

While certain proposals directly affect Social Security, such as ending taxes on benefits or certain kinds of income, other policies, such as curbing immigration, would also have consequences for the program, he said.

"It is such a large program that any policy that changes the economy or the tax code is likely to have some effect on Social Security," Biggs said. "And likewise, Social Security is so big, any changes to Social Security will affect other things."

With Social Security's funding depletion dates approaching, both campaigns could provide more details on how they would reform the program, he said.