The most troublesome tax increases in Barack Obama’s plan are not those we can already see but those sure to be announced later, after the election is over and budget realities rear their ugly head.

The new president, whoever he is, will start out facing a budget deficit of at least $1 trillion, possibly much more. Sen. Obama has nonetheless promised to devote another $1.32 trillion over the next 10 years to several new or expanded refundable tax credits and a special exemption for seniors, according to the Urban Institute and Brookings Institution’s Tax Policy Center (TPC). He calls this a “middle-class tax cut,” while suggesting the middle class includes 95% of those who work.

Mr. Obama’s proposed income-based health-insurance subsidies, tax credits for tiny businesses, and expanded Medicaid eligibility would cost another $1.63 trillion, according to the TPC. Thus his tax rebates and health insurance subsidies alone would lift the undisclosed bill to future taxpayers by $2.95 trillion — roughly $295 billion a year by 2012.

But that’s not all. Mr. Obama has also promised to spend more on 176 other programs, according to an 85-page list of campaign promises (actual quotations) compiled by the National Taxpayers Union Foundation. The NTUF was able to produce cost estimates for only 77 of the 176, so its estimate is low. Excluding the Obama health plan, the NTUF estimates that Mr. Obama would raise spending by $611.5 billion over the next five years; the 10-year total (aside from health) would surely exceed $1.4 trillion, because spending typically grows at least as quickly as nominal GDP.

A trillion here, a trillion there, and pretty soon you’re talking about real money. Altogether, Mr. Obama is promising at least $4.3 trillion of increased spending and reduced tax revenue from 2009 to 2018 — roughly an extra $430 billion a year by 2012–2013.

How is he going to pay for it?

Raising the tax rates on the salaries, dividends and capital gains of those making more than $200,000-$250,000, and phasing out their exemptions and deductions, can raise only a small fraction of the amount. Even if we have a strong economy, Mr. Obama’s proposed tax hikes on the dwindling ranks of high earners would be unlikely to raise much more than $30 billion-$35 billion a year by 2012.

Besides, Mr. Obama does not claim he can finance his ambitious plans for tax credits, health insurance, etc. by taxing the rich. On the contrary, he has an even less likely revenue source in mind.

In his acceptance speech at the Democratic convention on Aug. 28, Mr. Obama said, “I’ve laid out how I’ll pay for every dime — by closing corporate loopholes and tax havens.” That comment refers to $924.1 billion over 10 years from what the TPC wisely labels “unverifiable revenue raisers.” To put that huge figure in perspective, the Congressional Budget Office optimistically expects a total of $3.7 trillion from corporate taxes over that period. In other words, Mr. Obama is counting on increasing corporate tax collections by more than 25% simply by closing “loopholes” and complaining about foreign “tax havens.”

Nobody, including the Tax Policy Center, believes that is remotely feasible. And Mr. Obama’s dream of squeezing more revenue out of corporate profits, dividends and capital gains looks increasingly unbelievable now that profits are falling, banks have cut or eliminated dividends, and only a few short-sellers have any capital gains left to tax.

When it comes to direct spending — as opposed to handing out “refund” checks through the tax code — Mr. Obama claims he won’t need more revenue because there will be no more spending. He even claims to be proposing to cut more spending ending up with a “net spending cut.” That was Mr. Obama’s most direct answer to Bob Schieffer, the moderator of the last debate, right after Mr. Schieffer said “The nonpartisan Committee for a Responsible Federal Budget (CFARB) ran the numbers” and found otherwise.

When CFARB “ran the numbers,” they relied almost entirely on unverifiable numbers eagerly provided to them by the Obama campaign. That explains why their list of Mr. Obama’s new spending plans is so much shorter than the National Taxpayers Union fully documented list.

But nothing quite explains why even the vaguest promises to save money are recorded by CFARB as if they had substance. Mr. Obama is thus credited with saving $50 billion in a single year (2013) by reducing “wasteful spending” and unnamed “obsolete programs.” He is said to save Medicare $43 billion a year by importing foreign drugs and negotiating bargains from drug companies. Yet even proponents of that approach such as the Lewin Group find that cannot save more than $6 billion a year. So the remaining $37 billion turns out to depend on what the Obama campaign refers to as undertaking “additional measures as necessary” (more taxes?).

The number of U.S. troops in Iraq will decline, regardless of who the next president is. Yet the CFARB credits John McCain’s budget with only a $5 billion savings from troop reduction in Iraq, while Mr. Obama gets an extra $55 billion.

Straining to add credibility to Mr. Obama’s fantasy about discovering $75 billion in 2013 from “closing corporate loopholes and tax havens,” CFARB assures us that “the campaign has said that an Obama administration would look for other sources of revenue.” Indeed they would.

In one respect, CFARB is more candid than the Obama campaign. Mr. Obama favors a relatively draconian cap-and-trade scheme in which the government would sell rights to emit carbon dioxide. The effect on U.S. families and firms would be like a steep tax on electricity, gasoline and energy-intensive products such as paper, plastic and aluminum. Whenever Mr. Obama claims he has not (yet) proposed any tax increase on couples earning less than $250,000, he forgets to mention his de facto $100 billion annual tax on energy. (The McCain-Lieberman cap-and-trade plan is more gradual and much less costly.)

CFARB assumes Mr. Obama’s cap-and-trade tax would raise $100 billion in 2013 alone, but the actual revenue raised would be much lower. Like every other steep surge in energy costs, the Obama cap-and-trade tax would crush the economy, reducing tax receipts from profits and personal income.

The Joint Tax Committee reports that the bottom 60% of taxpayers with incomes below $50,000 paid less than 1% of the federal income tax in 2006, while the 3.3% with incomes above $200,000 paid more than 58%. Most of Mr. Obama’s tax rebates go to the bottom 60%. They can’t possibly be financed by shifting an even larger share of the tax burden to the top 3.3%.

Mr. Obama has offered no clue as to how he intends to pay for his health-insurance plans, or doubling foreign aid, or any of the other 175 programs he’s promised to expand. Although he may hope to collect an even larger share of loot from the top of the heap, the harsh reality is that this Democrat’s quest for hundreds of billions more revenue each year would have to reach deep into the pockets of the people much lower on the economic ladder. Even then he’d come up short.

This commentary was adapted from a paper for Hillsdale College’s Free Market Forum.