The idea of debt-free college is picking up steam on the 2016 campaign trail, but New Jersey Gov. Chris Christie, a likely Republican presidential contender, doesn't think it's the best way to solve the college affordability problem.

Before introducing his ideas to reform the nation's higher education system during a speech at Iowa State University on Thursday, Christie recounted the story of how his father, who graduated at the top of his high school class, was unable to accept his offer of admission to Columbia University because the school was too expensive.

After being drafted into the Army during the Korean War and subsequently working at a Breyers ice cream plant in Newark, New Jersey, a coworker convinced him to return to school using the G.I. Bill.

Over the next six years, Christie said, his father was able to complete his degree while working part time to support himself financially. That model, Christie continued, is how higher education in America is "supposed to work – a system where we all need to take personal responsibility to grasp the opportunities of higher education, but also one where we can get a leg up when we need it."

It's no surprise, then, that Christie also used his speech as an opportunity to criticize the growing fanfare around the idea of debt-free – or tuition-free – college.

"That is a typical liberal approach," Christie said. "It is wrong, and we know it. There are always costs involved, and if college graduates are going to reap the greater economic rewards and opportunities of earning a degree, then it seems fair for them to support the cost of the education they're receiving. Earning a degree should actually involve earning it."

Democrats, including Sens. Elizabeth Warren of Massachusetts and Harry Reid of Nevada, have propelled the idea of debt-free college into the national spotlight.

Warren on Wednesday detailed a path toward creating debt-free options for students, one with different components to hold schools, states and the federal government accountable for the cost and quality of higher education.

Warren's plan would hold colleges at least partly responsible when graduates default on their student loans – a risk-sharing idea that's been discussed in the Senate education committee as Congress embarks on the lengthy process to reauthorize the Higher Education Act, and one Warren said would force schools to "put some skin in the game."

She also would push states to maintain minimum levels of support for higher education and provide student loan refinancing options, while the federal government would use its leverage to financially support states if they keep costs down and improve student outcomes, and if they simplify the application process for federal student aid.

"While not every college needs to graduate every student debt-free, every kid needs a debt-free option – a strong public university where it's possible to get a great education without taking on loads of debt," Warren said Wednesday. "It's time to open the doors of opportunity wider and to invest in our future."

Also on Wednesday, 5,000 political leaders nationwide signed on to the Progressive Change Campaign Committee's Ready for Boldness campaign urging Democrats to run for office on populist ideas, including debt-free college.

Democratic presidential contenders Hillary Clinton and former Maryland Gov. Martin O'Malley already have said they plan to make debt-free college part of their campaigns, although there isn't a clear consensus on what such a model would look like among the party's White House hopefuls. While Sen. Bernie Sanders has introduced legislation to make four-year public colleges tuition-free, Clinton has yet to reveal a concrete debt-free college plan, though Politico reported Thursday that her blueprint may be influenced by Warren.

Lawmakers on both sides of the aisle recognize the issues surrounding college affordability – it's no secret that tuition rates have skyrocketed, and that a college education is becoming increasingly out of reach for more students.

"So for too many students, they're caught between a rock and a hard place," Christie said. "They can go to college, struggle to get by and face crippling debts. Or they can not go to college – and face the loss of economic opportunities and mobility that comes from that."

Unsurprisingly however, the two parties disagree on how to solve the problem.

Democrats, as Warren pointed out Wednesday, focus on resources, often citing state budget cuts as a primary factor in the increase of college costs. Republicans, on the other hand, don't want to allocate more federal funds to the issue without ensuring states and colleges will try to keep costs down and quality up on their own.

Republicans, including Christie, have said efforts to improve college affordability should target the lowest-income students. During his speech, Christie suggested increasing funding for certain financial aid avenues – like the Federal Supplemental Educational Opportunity Grant program and Perkins Loans – along with giving students grants in exchange for community service and using income-share agreements.

The latter is an idea that Republican Sen. Marco Rubio of Florida, another presidential candidate, has proposed through federal legislation, and centers around outside groups financing a student's education. Rather than paying back a loan amount, the student would pay the investor a percentage of his or her income for a set period of time. Theoretically, investors would have an incentive to help students find a pathway to a career and to continue to counsel them after graduation.

"With traditional private loans, students whose degrees don't pay off can wind up getting stuck with crippling repayments," Christie said. "But with an income-share agreement, there's no lump sum to repay and so there's very strong downside protection for students."

The agreements "have the potential to stem tuition inflation and reward high-quality but lower-cost programs," Christie said.

Christie also emphasized the need for more innovation in higher education, and pushed the idea of expanding the model beyond a traditional four-year institution through increased apprenticeships, allowing students to earn credit for prior learning and professional and military experience, and improving job training in high schools and community colleges.