Three years ago, Trump became the first Republican to win Michigan, Wisconsin and Pennsylvania in decades, in part on the strength of his performance among a handful of voters who had backed former President Obama in 2012.

Two-thirds of those Obama-Trump voters say they see Trump favorably heading into his reelection campaign — but that number has fallen by 19 percentage points since 2016, according to a new survey by the Voter Study Group.

Obama-Trump voters tend to be disproportionately located in the Midwest. They are most likely to be members of the white working class who never attained a college degree, said Robert Griffin, the Voter Study Group’s research director.

Political scientist John Sides has found that about 9 percent of Obama voters chose Trump over Democratic nominee Hillary Clinton in 2016, or about 5 percent of the overall electorate.