The tax and spending plans put forward by the five remaining presidential candidates don't add up, former U.S. Comptroller General David Walker said Monday.
Walker noted that Democrats Hillary Clinton and Sen. Bernie Sanders would mostly build on the current tax system, while Republicans would comprehensively reform it, either by imposing a flat tax or broadening the base and reducing the top marginal rate.
The problem is the spending side, said Walker, who worked under presidents Bill Clinton and George W. Bush and is now a strategic advisor at PricewaterhouseCoopers.
"That's where we have a problem, OK? Because nobody's numbers add up, or come close to adding up," he told CNBC's "Squawk Box."
Ohio Gov. John Kasich has provided a framework for balancing the budget within two terms, but Walker said the outline lacks details with regard to social insurance programs and other spending.
"He's got a track record of being able to do that, but candidly, it's just a framework," he said.
As a former U.S. congressman and chairman of the House Budget Committee, Kasich introduced welfare reform that President Clinton ultimately signed, and was a key figure in the deal passing the Balanced Budget Act in 1997.
The United States needs comprehensive tax reform that makes the country's code more simple and fair, generates more revenue and improves America's competitive posture, Walker said.
The new tax code should incentivize long-term planning and be paired with public-private partnerships and a comprehensive infrastructure strategy, he added.
Overall, politicians should think in terms of debt as a percent of GDP, rather than focusing on absolute debt and deficit figures, Walker said.
"That is a pro-growth strategy, but fiscally responsible. And it's a show-me test. If it works, you know it," he said.
No Labels, the bipartisan group Walker co-founded, has compiled a list of 60 initiatives to promote job growth, fiscal responsibility, Social Security and Medicare solvency and energy security. The group says the initiatives all have a super majority of support among Americans.
"What we need is what we haven't had for many years: leadership. And we need to listen to the American people and find out what they're willing to accept because the special interests will never get us to where we need to be," he said.