The last seven weeks amount to a sea change in U.S. economic policy. The era of fiscal austerity is over, and the era of big deficits is back. The trillion dollar question is how it will affect the economy.

In the short run, expect some of the strongest economic growth the country has experienced in years and some subtle but real benefits from a higher supply of Treasury bonds in a world that is thirsty for them.

In the medium run, there is now more risk of surging inflation and higher interest rates — fears that were behind a steep stock market sell-off in the last two weeks.

In the long run, the United States risks two grave problems. It may find itself with less flexibility to combat the next recession or unexpected crisis. And higher interest payments could prove a burden on the federal Treasury and economic growth.

It’s hard to overstate how abrupt the shift has been.

When the Congressional Budget Office last forecast the nation’s fiscal future in June, it projected a $689 billion budget deficit in the fiscal year that begins this coming fall. Analysts now think it will turn out to be about $1.2 trillion.

One major reason is the tax law that passed Dec. 20, which is estimated to reduce federal revenue by about $1.5 trillion over the next decade. A budget deal passed in the early hours Friday includes $300 billion in new spending over the next two years for all sorts of government programs and $90 billion in disaster relief.

It is a stark reversal from 2010 to 2016.

Congressional Republicans insisted upon spending cuts and the Obama administration insisted on raising taxes. Those steps, combined with an improving economy, cut the budget deficit from around 9 percent of gross domestic product in 2010 to 3 percent in 2016.

The near term:

In almost any economic model you choose, the new era of fiscal profligacy will create a near-term economic boost. Economists generally think these policies will have a lower “multiplier” than these policies would have if they took place during a recession, when there is more spare capacity in the economy.

“Some people assume that because this was a bad process and the tax bill is really regressive that it won’t have a short-term growth impact, but I think that’s wrong,” said Adam Posen, president of the Peterson Institute for International Economics.

The medium term:

Over the next two or three years, things get more murky. The big question is whether the economy has the room to keep growing without higher inflation emerging. The unemployment rate is already low at 4.1 percent. That means there is a chance that all this extra money flooding into the economy doesn’t go toward more economic output but just bids up wages and ultimately consumer prices.

The Federal Reserve would almost certainly raise interest rates more than it now plans, essentially engineering an economic slowdown to try to keep inflation from accelerating. In that scenario, the apparent benefits of tax cuts and spending increases would be short-lived.

But there’s no certainty that will happen. Perhaps corporate income tax cuts and looser regulation on business will unleash more capital investment and higher productivity, as conservatives argue.

The long run:

The Congressional Budget Office projected last June that the nation’s debt-to-GDP ratio would rise to 91 percent in 2027, from 77 percent in 2017.

The CBO hasn’t updated those numbers to reflect the new tax and spending legislation, but the Committee for a Responsible Federal Budget estimates that it will turn out to be between 99 and 109 percent.

The effects of higher debt service costs are one big one. Taxpayers in 2027 were forecast to pay $818 billion a year in interest costs even before the tax cuts and spending increases,. That will presumably be higher, both because taxpayers will be paying interest costs on more debt and probably at higher interest rates.

There is probably some point at which the amount of debt the government takes on crowds out private investment; to the degree that the supply of funds to borrow is finite, every dollar the government borrows is not available to be lent to a homeowner taking out a mortgage or a business looking to expand. That said, in practice, the supply of loanable funds is not finite.

The bigger costs of a high national debt may come in how much flexibility policymakers have to respond to a future recession or crisis.