The CBO says it would add $3.4 trillion to the deficit over the next decade. For decades, fiscal hawks have warned about the devastating consequences of ballooning U.S. debt. But economists say this time around is different: The debt is now so large that piling more on top of it as part of President Donald Trump's massive tax cut and spending bill could set the country on a dangerous path.

At nearly 900 pages, the legislation is a sprawling collection of tax breaks, spending cuts, and other Republican priorities, including new money for national defense and deportations.