From the very beginning, Trump has said that he's always gotten along with everybody -- he's donated to Democrats and Republicans, liberals and conservatives, everybody. He's deplored how polarized the country has become, where Democrats and Republicans both think the other side is not merely an opponent in an electoral contest, but the evil enemy. And he's repeatedly assured us that he's going to be a unifier, and that he's going to unite the country, so that members of the two parties won't be totally alienated from each other.
None of the other Republicans have campaigned with this message, either now or any time in recent memory. Their goal is instead to unite the Republican party, and to wage war against the evil enemy in the general election, whether or not they win (they usually don't).
Since Trump has placed unity of the nation over unity of one of its parties, it stands to reason that he'll make "getting along with Democrats" a theme of his general campaign. Not the Democrat Establishment, of course, but the good Democrats, the ones who want to make America great again. Trump will further marginalize Crooked Hillary by declaring that she can keep the bad Democrats -- the SJW crowd and the Wall Street lobbyists -- and because Trump is not riding on the backs of a wacko culture war group itself (unlike Cruz would be doing), she won't be able to respond by marginalizing him and his supporters.
Openly courting the "honest Democrats," along with those who normally wouldn't be voting at all, avoids the moronic strategy that the Republicans have been losing with for 25 years -- "hammering the swing voters". Nobody can be on the fence between Trump and Crooked Hillary, so anyone who is, must have no principles or goals or intuition. They're going to flip a coin on election day, so why waste so much time, money, and effort trying to budge them?
Courting honest Democrats by defending most aspects of Planned Parenthood, keeping Social Security as is, blasting George W. Bush's entire legacy, and so on and so forth -- that's how you win an election. Convert those who would normally be on the other side, and get more people off of the sidelines and into the arena. Unlike unmovable swing voters, these folks have clearly defined things they care about, and if you give them reason to believe you'd do well for those things, you're in the running.
Best of all -- they're way more than 3% of the population. Convert them, and you win in a landslide. Not just barely winning if you manage to convince every single swing voter.
This doesn't require tons of time, money, and effort -- only a shift in the policies that your party would normally be advocating (and losing with). Only blind adherence to a failed ideology (GOP conservatism today, or Dem liberalism in the '70s and '80s), prevents candidates from simply changing their platform in order to broaden their appeal and actually win control of the government.
Still, persuading members of the other party that you're going to do better for their interests than the candidate of their usual party, is going to be a tough sell. They'll want unfakeable signals of good faith. Trump already has established his long past of relating well with Democrats and Republicans, not only personally but politically. What can he do, though, as a promise about the future?
He could name honest Democrats as members of his Cabinet, and as heads of other important federal agencies. (He's said his Supreme Court picks will be fairly conservative, so that would probably exclude any Dems.) There aren't many Dems who would overlap with his plan entirely, but maybe on one or two aspects -- in which case, assign them to the head of the relevant agency, where they couldn't compromise his plan in the domains where they don't agree.
They would not be tokens, an empty symbol of bipartisanship, but one of the best people for that job. Probably the best person to begin busting up Wall Street banks is not a Republican. And probably the best person to deport illegals and anchor babies is not a Democrat. But it's OK if some jobs will be best done by Dems and others by Repubs.
"Here's the story, folks: I only hire the best people, it has nothing to do with what party they belong to. And if it turns out they're not doing the best job, I'm gonna say -- YOU'RE FIRRRED!"
Poaching the best Democrats ahead of the election will not only persuade the voters that he's already President, it will be an unfakeable sign of good faith to the would-be Hillary voters that he's serious about wanting everybody, regardless of party, to join his team for the greater good of the nation.
So, who are some of the good Democrats that Trump could appoint to one post or another? They wouldn't have to be currently serving, of course. I know even less about them than I do about the universe of Republicans he is recruiting from. But they've got to be there somewhere.
Related: a few earlier posts here and here about what role Bernie could play in a Trump administration, and how it could help in the general election.