“So where else is he going to go?” says Professor Sabato, editor in chief of the political site Crystal Ball. “He’s left with gubernatorial candidates.”

Take solid-blue Connecticut. Governor Malloy won four years ago by less than half a percentage point. Now he’s in a rematch against the same opponent, Tom Foley, a businessman and former US ambassador to Ireland. Malloy’s not especially skilled at public speaking, and so having Obama, who is, cheerlead for him could help.

Maine is another interesting case. The incumbent governor, tea party-backed Republican Paul LePage, won four years ago with just 38 percent of the vote in a multi-candidate race. This year, independent candidate Eliot Cutler is running again, but analysts expect many of his voters to go for the Democrat, Rep. Mike Michaud, to prevent Governor LePage from winning again. Obama won Maine in 2012 with 55 percent of the vote.