Mr. Biden, 77, and Mr. Sanders, 78, have both faced questions about their ages in recent days, as the race has narrowed to two men who would turn 80 within the space of a first presidential term — and as fears of a viral epidemic have rippled through the campaign trail. And supporters of Mr. Sanders have been sharply critical of Mr. Biden for his halting public manner and comparatively brief remarks at campaign events, with some suggesting that the former vice president lacked the physical vigor required to win and hold the presidency.
Mr. Sanders himself has not gone that far, though in a Fox News forum on Monday he criticized Mr. Biden for speaking for only a few minutes at one of his campaign rallies over the weekend.
For the most part, Mr. Sanders has avoided clashing harshly with Mr. Biden, even as his own position in the race has diminished. A particularly stark illustration of that dynamic came on Saturday night, when aides to Mr. Sanders advised reporters that the senator would be taking on Mr. Biden’s record on race at a campaign event in Flint, Mich. But Mr. Sanders did nothing of the kind, delivering a standard stump speech instead.
A day later, Mr. Sanders used a Fox News forum to deliver a critique of Mr. Biden’s record, but emphasized he had no interest in “making personal attacks on Joe.” He pointed to Mr. Biden’s vote to authorize the 2003 invasion of Iraq; his past support for the Hyde amendment, which restricts the use of government funds for abortion; and his history of seeking to rein in certain popular government programs.
“Joe has been on the floor of the House, over the years, talking about the need to cut Social Security, veterans programs, other programs,” Mr. Sanders said. “I have led the opposition to those cuts.”
Mr. Sanders’s campaign has been hopeful that Mr. Biden’s record, especially on trade, could undermine his popularity in the industrial Midwest, starting in Michigan, and it is airing ads highlighting his support for Nafta. But if those attacks prove fruitless in Michigan, they may be just as ineffective when Ohio and Wisconsin Democrats go to the polls in the coming weeks.