Democratic voters concerned about President Joe Biden’s age have cast a shadow over his 2024 campaign as the party’s nominating process begins.

Over half of Biden’s voter base, 54%, say they have major or moderate concerns about whether the Democratic president has the mental and physical health to hold office when asked about his age, according to a national NBC News poll released Tuesday. Sixty-two percent of total respondents reported they have “major concerns” about Biden’s age and health.