This is what I'd say to Bernie:
"Bernie, pal, look. This is all very clear-cut here. First of all, don't even start with me about you winning the nomination. You lost. The question is what you're going to do now. And what you do know will determine how you're going to be remembered.
"Second: we've already given you a lot at the Convention, and you've responded by punching us in the face. And, you know -- reaching out a friendly hand and getting kicked in the teeth for it tends to tick people off. It's time for you to give. And you know what we want. Get behind Hillary, and you'll be amazed at how quickly we're in a giving mood again.
"You have said that your positions are much closer to Hillary's than to Trump's. But unless I'm mistaken, it's been several months since you've said it publicly. The last time I can remember is the first debate. You said that the differences between you and Hillary, although they were important to you, were tiny not only compared to the differences between you and Trump, but also between you and anyone running for the Republican Presidential nomination.
"Did you actually stop believing that because of a Hollywood fund-raiser? You said that the price of admission to George Clooney's fundraiser was 'obscene.' I don't get that: when rich people like Hollywood superstars or Lehman Brothers give big checks to Democrats, it's obscene, but when some waitress gives you a check for $50 which she might not actually be able to afford, it's democracy.
"If you no longer believe that your positions are much closer to Hillary's than to those of the Republicans, then maybe there's nothing much more for us to talk about. But if you still believe that Hillary and the Democrats are much better than the Republicans, you can get behind us, and campaign hard for Hillary. When your die-hard supporters start booing as soon as you say her name, shout 'em down, tell 'em that all of this talk about her being a monster and a Republican in everything but name is nonsense, point out to them that when it comes to women's health and freedom to choose, green energy, tax breaks for Big Oil, labor unions, whether one fears that the government has too much control over corporations or that corporations have too much control over the government, whether the best way to help all of us is to help the poorest and weakest or the richest and most powerful, whether or not everyone should have access to affordable health care, whether too many tax breaks are available to corporate CEO's making 8 figures a year or more or to teachers and firemen making $50,000 a year or less, whether GLBT's don't have enough rights or whether they have too many, whether or not it's time to revoke the Civil Rights Acts of 1964 and 1965, whether or not drilling for oil and gas in national parks would be a good idea, and whether or not I'm a secret Kenyan Muslim Communist, there is a difference of night and day between Hillary and Donald, and between Hillary and most Republicans. Point out to them that the one single person who's done more than any other, going back to the early 90's, to get affordable health care to more people, is Hillary Clinton.
"If you fire up your supporters for Hillary, if you campaign hard for her and for down-ticket Democrats, then we're going to have a landslide in November. Not just Hillary winning by a mile, but also Democratic majorities in both houses of Congresses and in the Governors' offices and in mayoral offices and city councils and so on. We might have huge majorities. Imagine all the things a Democratic President could do with a filibuster-proof Democratic Congress backing her up. A Progressive Democratic Congress that keeps pulling her to the Left -- she'll go Left with you, it's not that far from where she was headed anyhow. Education and infrastructure would be restored, we'd convert from oil and coal and gas to solar and wind and geothermal, the air and water would get clean again, wages would go up, regulation would keep Wall Street in line, poverty and homelessness would plummet.
"Bernie, it would be beautiful. And you would be beloved, because everybody would know that you were a huge part of it.
"Or you can keep acting like a spoiled brat who can't admit that he lost, and continue to make everything harder for us, and you'll go down in history as an ultra-Nader. Hillary will still win, but those down-ballot Democratic majorities could vanish. Hillary could be faced with the same obstructionist Republican bullshit I've had to deal with. And people will realize that it was because of you. It'll take some time for some people to see it, the way it took some people some time to figure out what Nader did in 2000, but they'll figure it out. You'll be an ultra-Nader.
"Your power will fade very fast if you don't get with us. It already is fading: a lot of your biggest former backers are already publicly behind Hillary. They didn't wait for you to come to your senses. If you continue to fight her, pretty soon your support will have shrunken down to a hard-core of low-information voters, or non-voters. Haters. Mysogynists. I don't know: maybe those really are your people. Maybe you want to stick with them, and don't want to try to enlighten them about their actual choices in November. Maybe you like having those hard-care crazies and you against the world.
"You're gonna do what you're gonna do. You can be a huge part of a glorious victory, or you can continue to throw a tantrum because you didn't get everything you wanted, and sabotage all of your own causes, which are our causes too. Now get out of my Oval Office, I've got work to do. Decide whether you're my ally or my enemy."