NEW YORK — For one tiny sliver of swing voters, it is not enough to be wrestling with whether to vote for President Obama or Mitt Romney at a moment when nearly everyone else has long since decided. Their checkbooks, too, are wavering between the two candidates.

Meet the undecided donors. They are not lobbyists or other members of the political class — donors with a professional imperative to hedge their bets — but ordinary voters whose back-and-forth donations mirror the undulations of the swing electorate.