In the closing weeks of last year's election campaign, we wrote that Democrats had in mind the most sweeping expansion of government in decades. Liberals clucked, but it turns out even we've been outbid. With yesterday's fiscal 2010 budget proposal, President Obama is attempting not merely to expand the role of the federal government but to put it in such a dominant position that its power can never be rolled back.

The first point to understand is the sheer magnitude of federal spending built into this proposal. Federal outlays will soar in fiscal 2009 to $4 trillion, or 27.7 percent of GDP, from $3 trillion or 21 percent of GDP in 2008, and 20 percent in 2007. This is higher as a share of the economy than any year since 1945, when the country was still mobilized for World War II. It is more spending by far than during the Vietnam War, or during the recessions of 1974-75 or 1981-82.

But let's assume, for the sake of argument, that Mr. Obama is right that this spending is needed now to "jump-start" an economic recovery. Though the budget predicts that the economy will recover in 2010, spending will still be 24.1 percent of GDP that year, and the budget proposes that spending will remain higher than 22 percent for the entire next decade even as the defense budget steadily declines. All Presidential budgets predict spending will decline in the "out years," if only to give the illusion of spending restraint. Mr. Obama tries the same trick, but he is proposing so many new and expanded nondefense programs that his budgeteers can't get anywhere close even to Jimmy Carter spending levels.

These columns focus on spending, rather than deficits, because Milton Friedman taught us that spending represents the real future burden on taxpayers. Nonetheless, the 2009 budget deficit is estimated to be an eye-popping 12.7 percent of GDP, which once again dwarfs anything we've seen in the postwar era. The White House blueprint predicts that this will fall back down to 3.5 percent as soon as 2012, but this is based on assumptions about Washington that aren't going to happen.

For example, Mr. Obama's budget assumes that nearly all of the new stimulus spending will be temporary -- a fantasy. He also proposes to eliminate farm subsidies for those with annual sales of more than $500,000. This is a great idea, and long overdue. But has the President checked with Senators Kent Conrad, D-North Dakota, or Chuck Grassley, R-Iowa? We hope we're wrong, but a White House that showed no interest in restraining Congress during the recent stimulus bacchanal isn't likely to stand athwart history to stop the agribusiness lobby.

The falling deficit also assumes the largest tax increase in U.S. history, starting in 2011 with the repeal of the Bush tax rates on incomes higher than $200,000 for individuals and $250,000 for couples. The White House says this will yield upwards of $1 trillion, if you choose to believe that tax rates don't affect taxpayer behavior.

In the real world, two of every three tax filers who fall into this income category are small business owners or investors, who are certainly capable of finding ways to invest that allow them to declare less taxable income. The real impact of this looming tax increase will be to cast further uncertainty over economic decisions and either slow or postpone the recovery. Ditto for the estimated $646 billion from a new cap-and-trade tax, which no one wants to call a tax but would give the political class vast new leverage over the private economy.

Then there is Mr. Obama's plan for national health care. The White House has put a $634 billion place holder in the budget to pay for covering tens of millions of uninsured Americans with government subsidized coverage. But even advocates of this government plan say the cost will be closer to $1 trillion over 10 years, and probably much more. Meanwhile, the President is promising to reform entitlements, but his budget proposes a net increase of about $1 trillion in Medicare, Medicaid and other entitlements.

The biggest illusion in this budget may be its optimistic economic forecast. The White House assumes that the economy will decline by only 1.2 percent this year, before growing by 3.2 percent next year. This assumes the recovery will begin later this year and gather steam quickly to return to normal levels of growth. By 2010 to 2013, the budget adds, the economy will be cooking by an average of 4 percent a year -- which is also how it conjures up magical deficit reduction.

This growth is a lovely thought, but how? The only impetus for growth in this budget comes from the government spending more money that it is taking out of the job-producing private economy. With $1 trillion of new entitlements, $1.4 trillion in new taxes, and $5 trillion in new debt, America's entrepreneurs aren't getting any help soon from Washington.

Democrats will want to rush all of this into law this year while Mr. Obama retains his honeymoon aura and they can blame the recession on George W. Bush. But Americans are only beginning to understand the magnitude of Mr. Obama's ambitions, and how much of their own income will be required to fulfill them. Republicans have an obligation to insist on a long and considerable debate on all of this, lest Americans discover in a year or two that they live in a very different country.