WASHINGTON—The national debt and sustained federal budget deficits will hit the highest levels since World War II over the next decade, the Congressional Budget Office projected on Tuesday, following multiple rounds of tax cuts and continued increases in federal spending.

The government will spend $1 trillion more than it collects in 2020 and deficits will reach or exceed that threshold every year for the foreseeable future. As a share of gross domestic product, the deficit will be at least 4.3% every year through 2030. That...