Mr. Trump, however, at various times has said he would be open to cutting safety-net programs, only to have aides walk back those comments after the fact. “At the right time, we will take a look at that,” Mr. Trump said in January of cuts to Medicare, Medicaid and Social Security — a stance that Biden campaign officials said they planned to highlight in the coming months.

The Biden team also noted that a second Morning Consult poll released this past week showed that 46 percent of voters said they trusted Mr. Biden to protect Medicare and Social Security, compared with 41 percent for Mr. Trump.