WASHINGTON (AP) -- President Donald Trump repeated his attacks Monday against the chair of the Federal Reserve, demanding that the central bank lower its key interest rate to boost the economy.

Trump called Powell "a major loser" and said that energy and grocery prices are "substantially lower" and "there is virtually No Inflation." Yet Trump said the economy could slow without rate cuts.

Gas prices have fallen for the past two months, in part because oil costs have dropped on fears of slower growth, but food prices jumped in January and March and overall inflation remains above the Fed's 2% target.

Trump's comments drove the stock market and the dollar lower as investors in the U.S. and overseas grow increasingly wary about the economic standing of the U.S. On Friday, a top White House adviser said the administration is studying whether it can fire Powell, a move that would undermine the Fed's independence and likely send shock waves through global financial markets.

Markets, which had already been heading sharply lower Monday, tumbled further after Trump's post, with the broad S&P 500 stock index down 2% in early trading.

Trump's threats against Powell and his higher tariff policies have driven down the dollar and also pushed up the interest rate on 10-year Treasuries, which ticked higher to 4.35% Monday. Those rates are the benchmark for mortgage rates, meaning that borrowing costs to buy a house will likely stay elevated.

A drop in the dollar is unusual when stock prices fall and Treasury yields rise, because investors typically buy U.S. government bonds during market turmoil. Instead, they appear to be avoiding U.S. markets generally.

Trump lashed out at Powell on Friday and said he could fire him if he wanted, though it would likely touch off a legal battle that could go to the Supreme Court. Powell has said the president doesn't have the authority to fire him and has also made clear he won't step down until his term ends in May 2026.