Bernie Sanders said over the weekend that no matter what happens now his campaign represents the future of the Democratic Party and that the issues he has raised will from now on be debated within the Democratic mainstream.

On Face the Nation, while discussing his appeal among younger voters, he said,

I think the ideas we are talking about (are) what the American people and the people in the Democratic Party want to hear. . . We are the future of the Democratuc Party, so I’m very proud of where we are and look forward to fighting this out through California.

He went on to say that he expects key issues of his campaign to be represented in the platform of the Democratic nominee.

Should Hillary Clinton win the nomination, he continued, issues like a $15 minimum wage, climate change, guaranteed health care, getting big money out of politics, and free college tuition should be a part of her agenda.

Make no mistake, Sen. Sanders has done remarkably well and will have much to bargain with, notably his enthusiastic support (or not) for the Democratic ticket. On the other hand, should Clinton be the nominee, it will mean he has lost. And, to be clear, losing means not winning.

I hope Sen. Sanders drives a hard bargain for his support, and I hope Hillary Clinton pushes back equally hard because she could, if not careful, find herself in the position of trying to deliver on promises impossible to keep largely because a president is not a queen, Congress is not without power, and state governments have significant authority on a range of issues.

In any case, there will be many discussions about heady things between the two camps. That’s politics, and I mean that in a good way. If in the end Sanders decides that he did not receive sufficient consideration for his full-throated support, no one will able to force him to do anything. If his supporters stay home on Election Day, that is their right.

These possibilities would, however, be unfortunate outcomes for the future he claims to want.

Parties matter greatly in politics, especially in a two party system. And because there are only two parties, coalitions within parties are essential.

If Sanders and his followers want to be the future of the Democratic Party, they should understand that there will come a time when they need the support of Democrats who are not completely on side with their vision. They will want and need that support to create something new.

Parties support those within the group precisely because they believe they have enough in common to hold the coalition together. Members and groups within a party will give those they may disagree with on many issues a chance to lead because they see themselves as within the same group.

Should Sanders and company play too cute in the coming months, they might refrain from being too surprised when the next “progressive” standard bearer finds it hard to get traction with the broader party.

Securing the future frequently requires playing nice with others, which can be very demanding. And if factions can’t be effectively managed, turnabout is always fair play, and usually ugly.