Statistician and writer Nate Silver raised multiple concerns for President Joe Biden’s re-election campaign on Monday, saying that Democrats appear to have no plans to address the issues.

In his “Silver Bulletin” newsletter on Monday, the co-founder and former editor-in-chief of polling analysis site FiveThirtyEight wrote that his outlook on the potential rematch between 81-year-old Biden and former President Donald Trump, 77, has significantly changed since a year ago. Silver circled Biden’s age and his refusal to sit down for big interviews, such as the traditional Super Bowl interview, as top concerns for his campaign.

“If you’d asked me a year ago, I would have told you that Joe Biden was a reasonably clear favorite in the event of a rematch against Donald Trump,” Silver began, adding later in his article that in recent months, “Biden’s situation has become considerably worse.”

“If he were 10 years younger, he might still be a 65/35 favorite,” Silver wrote. “But if his campaign is substantially encumbered by his age, he’s probably the underdog.”

Silver’s latest piece on Biden’s vulnerability follows a newsletter he wrote in November when he suggested that for Democrats to win in 2024, the party should consider pushing a different candidate if Biden doesn’t “run a normal campaign.”

“Personally, I crossed the rubicon in November, concluding that Biden should stand down if he wasn’t going to be able to run a normal reelection campaign — meaning, things like conduct a Super Bowl interview,” Silver wrote on Monday. “Yes, it’s a huge risk and, yes, Biden can still win. But he’s losing now and there’s no plan to fix the problems other than hoping that the polls are wrong or that voters look at the race differently when they have more time to focus on it.”

Trump continues to lead the president in the national polling average, according to RealClearPolitics and FiveThirtyEight as Biden also faces low favorability ratings. Silver pointed to special counsel Robert Hur’s report on Biden’s handling of classified documents, which called the president a “well-meaning, elderly man with a poor memory.”

“Biden is probably a below-replacement-level candidate at this point because Americans have a lot of extremely rational concerns about the prospect of a Commander-in-Chief who would be 86 years old by the end of his second term,” Silver wrote. “It is entirely reasonable to see this as disqualifying.”