A trillion here and a trillion there — pretty soon, it’s real money!

Some of these are good ideas. Some aren’t. But most are popular, especially among Biden’s progressive and liberal supporters, and they are not free.

From a variety of sources — campaign releases, independent analyses, media stories and the Congressional Budget Office — I have constructed a rough estimate of what it would cost to cover all the new benefits. The additional 10-year spending totals $7.74 trillion. Here’s a breakdown:

2. Health care: $1.5 trillion

3. Climate change: $2 trillion

TOTAL: $7.74 trillion

But wait, we’re not finished yet. To these costs ought to be added the projected budget deficits under existing policies. For the period from 2021 to 2030, CBO figures that’s another $13 trillion. The grand total comes to $20.7 trillion (the $13 trillion, plus the $7.7 trillion).

Even for Washington, this is a lot of money. It brings to mind the quip commonly attributed to Republican Sen. Everett Dirksen of Illinois: “A billion here, a billion there, and pretty soon you’re talking about real money.” Substitute “trillion” for “billion,” and that’s where we are today.

The amounts are so stupendous that it’s hard for ordinary people to discuss them intelligently. Still, let’s try. Let’s concede that these estimates are very preliminary. They could be off by a few trillion dollars. But the error could be an underestimate of debt, not an overestimate.

Here’s an example: To his credit, Biden has proposed a tax increase to help close the budget deficits. In an exhaustive analysis, the Committee for a Responsible Federal Budget, a nonpartisan watchdog group, projected that the tax increases would amount to $3.35 trillion to $3.67 trillion over the decade. Most would fall on the top 1 percent, whose tax increases would average $300,000 annually.

But I have already incorporated this extra tax revenue on the assumption that a Democratic-controlled Congress would do most of Biden’s bidding. His larger purpose is clear: to buy peace among the so-called progressive and liberal wings of the party by endorsing many of their expensive proposals. The amounts are gigantic. For example, the $8 trillion is roughly equivalent to half the existing federal debt held by the public.

There must be some means of paying for these proposals. There are three basic choices, or some combination of them: (1) borrow the money — that is, further run up deficits and debt; (2) cut other programs, from defense to farm subsidies to Social Security; (3) raise taxes. It seems inevitable that some — or all — of these proposals will have to be scaled back.

I’m not saying it’s impossible to finance all these programs. But it is next to impossible. It’s true that many economists, including some of the heavy hitters, have concluded that the United States (and some other countries) can borrow indefinitely as much as it wants by selling Treasury securities. The argument, simplified, is that low interest rates make it easier for the United States to repay its debts and, therefore, reassure lenders that it’s okay to lend.

It’s politically expedient to borrow, because the costs are less visible than either higher taxes or spending cuts. But this argument comes with a large historic caveat: In the 1970s and early 1980s, many economists argued that “a bit more inflation” wouldn’t hurt the economy. But repeated episodes of “a bit more inflation” evolved into “a lot more inflation” — by 1980, consumer prices were rising at about 13 percent a year — that clearly hurt the economy. The same might be true of debt financing. At some point, rising deficits might become unsustainable and trigger a backlash from lenders. They cut their lending; interest rates rise.

All that seems certain is that the size of government will grow, reflecting the aging of society and the clamor for more spending for “worthy” causes. Between 2020 and 2030, Social Security and Medicare spending, as a share of the economy, is projected to grow by almost one third. If Biden wins, he and his advisers will have plenty to keep them awake at night.

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