Investors have all but concluded the Federal Reserve will raise interest rates next week for the first time in three years. The harder question is what comes after that.

Because almost no one at the central bank thinks a quarter-point increase will do much on its own to bring inflation down, a decision to raise rates next week would reflect a judgment that interest rates have been in the wrong place. If that is the case, one increase won't fix it.

The Fed rarely moves until officials are convinced one move won't be enough. "If we get a hike next week, certainly we'll get additional ones," said Richard Clarida, a former Fed vice chair who is now at Pimco.

Raising rates seven weeks before the midterm elections would be complicated enough. Setting the Fed on a course for more would be harder still. President Trump, who picked Federal Reserve Chairman Kevin Warsh partly because he expected an easier relationship than he had with Jerome Powell, has said he expects the new chairman to deliver lower rates.

Other senior officials have also pressed the issue. Vice President JD Vance said last week the administration would welcome help from the Fed on rates, and Treasury Secretary Scott Bessent has argued that recent inflation reflects a supply shock the Fed shouldn't be tightening into.

Since the Fed identified the federal-funds rate as its primary tool for shaping borrowing costs in the 1990s, the U.S. central bank has only once raised rates in a one-and-done fashion, in 1997. A likely move next week, Clarida predicted, "is certainly not one and done."

Warsh gave investors reason to think the same when he said in July he doesn't put much stock in the Fed's ability to steer the economy with small adjustments. "I don't think we're great in the fine-tuning business," he said. A chairman skeptical of fine-tuning is an unlikely candidate to raise rates a quarter point and declare the job done, analysts said Friday.

Fed governor Christopher Waller made the same point last week while outlining scenarios under which the Fed could afford to wait: Raising rates by a quarter point at one single meeting versus another isn't going to bring inflation down to 2%.

"Once you make the decision to tighten, you're going to move up enough that you feel like you've changed the level of restriction in a meaningful way," said Kurt Lewis, a former senior Fed adviser who is a strategist at Piper Sandler.

Waller's conditional case last week for holding rates steady, as officials did in July, rested on the Fed's forecast. Officials projected in June that monthly inflation would slow in the second half of the year as tariff effects rolled off, and June and July validated it. Friday's report went the other way: A key measure of underlying consumer prices was firmer than expected in August. It followed better news on hiring and renewed rises in oil prices from tensions in the Persian Gulf.

The decision between raising rates or holding steady "has been a close call for a long time," said Lewis. Friday's report "was the straw that broke the camel's back."

As a result, investors this week stopped treating September as a question about one meeting. Expectations for cumulative rate increases through next June rose to at least three, up from two. Before this week, swings in interest-rate markets had moved the timing of increases while leaving the endpoint alone.

Warsh laid the groundwork to argue that rates were in the wrong place during his keynote at Jackson Hole, Wyo., last month. He said he saw little evidence that borrowing conditions were restraining the economy and that the better inflation readings in June and July hadn't convinced him the underlying trend was improving.

A move justified on those grounds invites the obvious follow-up: how much higher? Fed chairs have long dealt with this by explaining what a move is for-a recalibration, an insurance policy, a risk-management adjustment-without necessarily promising what comes next. Warsh has been reluctant to explain how the Fed arrives at its decisions and has argued for years that guidance ties the central bank's hands.

Without an explanation, a quarter-point increase can turn into something larger in the market's hands. "If you haven't socialized it, that raises the risk that your policy action will be extrapolated and therefore overdone," said Vincent Reinhart, chief economist at BNY Investments and a former director of the Fed's monetary affairs division.

Markets assume a first move means more are coming, he said, and they price in too many. Without guidance, "you can't tamp it down," Reinhart said.

The Fed has one instrument that could help to shape expectations next week. Four times a year, officials submit projections for growth, unemployment, inflation and where they expect interest rates to go. The anonymized forecasts, which Warsh declined to participate in during his first meeting in June, could show how many increases the committee has in mind.

"There will be more than the usual signal" in the projections, said Dean Maki, chief economist at hedge fund Point72 Asset Management.

Warsh could bound it further. If he said, for example, the increase was taking back some of last year's cuts, Maki said, investors would read it as two or three at most. "But it would cut against his notion that the Fed's job isn't to provide forward guidance of that type," he said.

Reinhart said he is concerned that markets are boxing the Fed into a rate hike it may not yet need to deliver. Investors have overreacted to energy-driven swings in inflation, in his view, and the slow-moving part of inflation has been coming down gradually, obscured by high-frequency moves in energy prices.

A rate increase could help settle longer-term yields, which have risen in recent weeks, said Ed Al-Hussainy, a fixed-income portfolio manager at Columbia Threadneedle Investments. Holding rates steady could make that selloff more disorderly if investors thought the Fed would tolerate higher inflation.

San Francisco Fed President Mary Daly has framed the Fed's choice as between two economies. In one, the shocks of the past two years roll through and the Fed's current setting is sufficient to bring inflation down. In the other, the shocks compound, inflation broadens, and the Fed needs a much larger adjustment than a quarter point. In early August, scenario one remained her base case, but the two have since moved closer together in probability, she said.

Daly said the second scenario could require more than small quarter-point adjustments and a departure from the gradualism that the Fed has traditionally used to feel its way through an uncertain economy.

Officials who have been eager to move have made the opposite argument from the same premise. "Earlier, gradual, incremental interest-rate increases are preferable, less disruptive, less costly than potentially later more abrupt interest-rate changes," said St. Louis Fed President Alberto Musalem, who supported a July rate rise, in a speech last month.

Their case rests less on the past three months than on what is ahead: high diesel prices driven by the Iran war that have yet to filter through shipping networks, new rounds of tariffs, an AI build-out straining electricity and technology supply chains, and lofty stock prices supporting consumer spending.

The probability that inflation will be meaningfully above the Fed's target in 12 to 18 months is now higher than the probability that inflation will converge back to the central bank's 2% target, Musalem said.