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."