CBO projects that this year’s budget deficit will clock in at roughly $2 trillion, some $400 billion more than it forecast in February and $300 billion larger than last year’s deficit. This is unprecedented when the economy is growing and defense spending is nearly flat. The deficit this fiscal year will be 7% of GDP, which is more than during some recessions.

CBO says deficits will stay nearly this high for years, and the total over the next decade is now expected to total $21.9 trillion compared to $19.8 trillion in its February forecast. Debt held by the public will grow to 122.4% of GDP in 2034 from 97.3% last year.

Notably, CBO’s revenue projections are little changed. Revenue is expected to total 17.2% of GDP this year—roughly the 50-year average before the pandemic, as the nearby chart shows. But CBO significantly revised up projections for federal spending. Outlays are now expected to hit 24.2% of GDP this year and average 24% over the next decade. Wow.

For perspective, consider that spending before the pandemic exceeded 24% only once since World War II—in 2009 amid the financial panic and the Obama-Pelosi “stimulus” binge. CBO notes that one culprit for the larger deficit this year is Congress’s recent military aid bill. But overall defense spending is still falling as a share of the economy and is expected to hit a postwar low of 2.8% of GDP in 2034.

Not so President Biden’s latest plans for student-loan debt transfer to taxpayers, which CBO estimates could cost $211 billion this year above what it estimated in February. This is on top of the hundreds of billions of dollars in student debt that Mr. Biden has already written down in part with his SAVE plan, which turns loans into de facto grants.

Spending on Affordable Care Act subsidies and Medicaid is also exceeding earlier projections owing to higher enrollment. CBO increased its ACA spending estimate by $22 billion for this year and $244 billion over the next decade. It also raised its ACA enrollment projection by four million for this year and an average of three million over the next 10 years.

That’s because the Inflation Reduction Act’s sweetened subsidies and a Biden Administration regulatory change increased eligibility for subsidies. CBO also notes that the recent surge in immigration—migrants qualify for premium tax credits—has boosted enrollment. The result: ACA subsidies this year will cost more than double pre-pandemic projections.

The end of the pandemic emergency was expected to cause Medicaid enrollment to plunge. That hasn’t happened, in part because Democratic-run states have been slow to remove able-bodied adults who are no longer eligible. CBO has thus increased its forecast for Medicaid spending by $50 billion in 2024 and $314 billion over the next decade.

Entitlement spending—which now includes student loans—is growing at a pace that is fiscally unsustainable. Financing these programs has also become more expensive owing to higher interest rates, which CBO also projects will need to stay higher for longer in order to subdue inflation. Spending on interest is now expected to be $1.02 trillion next year, exceeding $964 billion for defense.

CBO’s budget forecasts are getting progressively uglier, but it’s not because Americans aren’t paying their fair share in taxes. If spending as a share of GDP remained at the pre-pandemic average, the deficit would be roughly $890 billion this year and $13.4 trillion smaller than CBO’s 10-year projection. This would keep debt as a share of GDP at roughly 90%.

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Neither Mr. Biden nor Donald Trump talks about the national debt, perhaps because they might then have to do something about it. But a moment of tax truth at least will arrive at the end of 2025 when most of the 2017 Trump individual tax cuts expire.

Mr. Biden’s plan is to raise taxes by $5 trillion or more, which would put the overall federal tax burden above 20% of GDP, which is close to the highest in peacetime. That still won’t finance Mr. Biden’s spending ambitions, which will continue to cost trillions in future years even if he loses the election.

Mr. Trump says he wants to renew and maybe expand the Trump tax cuts, and the best way to finance that is by repealing the Biden spending blowouts in the Inflation Reduction Act, student-loan write-offs and pandemic-era welfare expansions. Failing to take on that challenge means either a monumental tax increase or a debt panic down the road.