Self-identifying Democrats in particular have soured on the car maker since Mr. Musk bought Twitter for $44 billion in late October, according to data from research firm Morning Consult.
Mr. Musk, who plays a large role in the public image of Tesla and now Twitter, on Nov. 7 urged voters to back Republicans in the midterm elections.
Net favorability is the percentage of respondents with positive perceptions of a brand minus the percentage with negative perceptions.
Tesla also has millions of active supporters online, as does Mr. Musk.
More than 94% of U.S. adults are now familiar with Mr. Musk, up from about 75% one year ago, according to Mr. Marlatt of Morning Consult.