Source: Flickr user

Aging baby boomers are turning 65 at a pace of 10,000 per day, and that poses a big problem for Social Security because payments made to retirees are funded by a shrinking pool of American workers.

The graying of America has Social Security predicting that its ability to pay full benefits to retirees could come under pressure as soon as 2034, and as a result, there's a raging debate around Social Security reform this election year.

Among presidential candidates who have weighed in with potential changes to sure-up the 80-year-old safety net, these four recommend reducing Social Security benefits to high-income earners.

Source: Flickr user Gage Skidmore.

No. 1: Jeb Bush
Jeb Bush believes that changing the full retirement age from 67 to some other number, potentially as high as 70, would give the most bang for the buck, but he also favors means testing that could reduce the amount that high income earners receive in Social Security in the future.

Bush points out that spending on government healthcare programs and Social Security has grown to almost half of federal spending from about one-sixth of spending in the mid-1960s. Absent change, he says that spending will double as a percentage of the economy by 2040.

Pushing back full retirement age could change that spending trajectory most, but implementing a new method for figuring out how much people receive at full retirement age may also help. Specifically, Bush thinks "we can change Social Security so that higher-income workers, who can afford to save for retirement on their own during their careers, get a smaller check when they retire. These kinds of reforms will ensure that Social Security remains stable over the next 75 years."

No. 2. Chris Christie
Chris Christie would gradually phase in a program that starts eliminating Social Security payments to single retirees when income heads north of $80,000. The plan is to apply a sliding scale to benefits for single high-income earners who haul in between $80,000 and $200,000 and eliminate benefits all together to those earning more than that. Christie has also said that the limits proposed for singles would be increased for married couples, but he hasn't said to what levels.

No. 3. John Kasich
Last fall, John Kasich asked a New Hampshire audience if anyone far from retirement would mind if they received a bit less in Social Security when they retired if it meant saving the system. One person spoke up against Kasich's idea, and Kasich humorously replied, "You'd get over it."

Kasich's off-the-cuff joke set off a firestorm, but that firestorm hasn't shifted Kasich's mind that major Social Security reform has to happen sooner, not later.

In December, Kasich discussed his plans for Social Security in Iowa, telling the Des Moines Register "high-income seniors are going to get less." He hasn't said how much less, but it's clear that high-income earners would pick up at least some of the tab for saving Social Security under Kasich.

Source: Flickr user Mark Nozell

No. 4. Marco Rubio
Marco Rubio maintains that Social Security is on an "unsustainable path" and that changing its direction is critical to the program's survival.

He thinks Social Security reform should include changing calculations that impact the amount of benefits high income earners will collect in retirement. By reducing the rate of growth of benefits for "upper-income" seniors, there's less risk that benefits will have to be cut for everyone.