Much-lower interest rates could bolster stock prices and give the economy a lift headed into the 2020 election, which would be good news for Mr. Trump. Absent any help, most economists expect that growth will gradually decline to just below 2 percent, as the short-term benefits of Mr. Trump’s 2017 tax cuts and higher government spending fade.

That could be problematic for the president, who promised to coax growth to 3 percent or more, well above the level economists see as sustainable given current demographic and productivity trends.

The Fed has insisted that it is independent of the White House and will set policy with an eye on the economy, not the political cycle. Congress has given the Fed two goals, maintaining maximum employment and stable inflation, but freedom in how it achieves them. It does so primarily by changing borrowing costs to stoke or slow borrowing and spending.

But it is currently making policy calls against a complicated economic backdrop.

The Fed has failed to sustainably hit its 2 percent inflation target since formally adopting it in 2012, and various measures of consumer and market inflation expectations have recently drifted lower. That creates a risk that price increases will become mired permanently below the central bank’s goal, leaving it with less room to cut interest rates — which include inflation — in a downturn.

Overall economic growth is also slowing from a stronger pace in 2018 and early 2019, though it remains close to the Fed’s estimate of its longer-run potential. That is consistent with what the policymakers expected: They have long believed that the economy would slow down once the effects of Mr. Trump’s tax cuts and higher government spending had played out.

But stock prices are soaring, and the housing market has stabilized as mortgage rates have fallen. While it is not obvious how or even whether the trade war will end, Mr. Trump has said that negotiators are making progress toward a first-phase deal with China.

Mr. Powell avoided tying the outlook for monetary policy too closely to the success or failure of those negotiations.