Sen. Joe Manchin III (D-W.Va.) told Democratic leaders Thursday he would not support an economic package that contains new spending on climate change or new tax increases targeting wealthy individuals and corporations, marking a massive setback for party lawmakers who had hoped to advance a central element of their agenda before the midterm elections this fall.

The major shift in negotiations — confirmed by two people familiar with the matter who spoke on the condition of anonymity to describe the talks — threatened to upend the delicate process to adopt the party’s signature economic package seven months after Manchin scuttled the original, roughly $2 trillion Build Back Better Act, which President Biden had endorsed.

But Manchin told Democratic leaders he is open to provisions that aim to lower prescription drug costs for seniors, the two people said. And the West Virginia moderate expressed support with Senate Majority Leader Charles E. Schumer (D-N.Y.), the party’s chief negotiator, for extending subsidies that could help keep health insurance costs down for millions of Americans, one of the sources said.

“Political headlines are of no value to the millions of Americans struggling to afford groceries and gas as inflation soars to 9.1 percent,” said Sam Runyon, a spokeswoman for Manchin. “Senator Manchin believes it’s time for leaders to put political agendas aside, reevaluate and adjust to the economic realities the country faces to avoid taking steps that add fuel to the inflation fire.”