Hey, Social Security-cutting “centrists” who think you need a new party to get what you want: Here’s what you want to think about — same-sex marriage.

Let me back up a bit. The Americans Elect third-party presidential campaign collapsed yesterday. And I’ll give third-party optimist Matt Miller credit for having the courage of his convictions: Even in the face of that fiasco, he’s willing to keep fighting for the cause. Why? “It has to do,” Miller says, “with changing the boundaries of debate” and that “it will take some force outside the current system to inject into the debate a bolder agenda to renew America.”

Now, I think we could have an empirical fight about whether Miller is correct that the five issues he lists, or a similar set of issues that the New York Times columnist and third-party enthusiast Tom Friedman could list, are in fact beyond “the boundaries of debate” currently. I certainly hear plenty of talk about tax reform, consumption taxes and entitlements reform. But I’ll be willing to stipulate, for the moment, that he’s correct.

The question is: How does one in the United States get his or her issues into the national debate — and, perhaps more importantly, get them enacted into law?

It seems to me that Miller, Friedman and others in their camp would do well to study the efforts of those who have brought marriage equality from political poison to an endorsement from the president of the United States in fewer than 20 years.

How did they do it? I see two tracks: interest-group politics and party politics. Some advocates worked independently of the parties — they rallied public opinion through whatever high-visibility platforms they had, raised money, supported politicians who would support them and opposed ballot measures that would harm their cause. Others worked primarily within the Democratic Party, allying themselves with others who might be less interested in that issue but were eager to find friends for their own interests. When Democrats let them down — and in the 1990s, for example, there was plenty of that — they persevered, trying hard to get the balance right so that they could demand more of their friends without inadvertently helping their foes. That’s hardly an easy thing to do — and it was particularly hard for a group that , 25 years ago, had “allies” who were barely willing to be seen with them in public.

But the Americans Elect crowd isn’t, as far as I can see, willing to engage in the difficult and often painful work of coalition politics. It’s not just that they believe that they are right. After all, practically everyone believes that his or her own positions on public policy are correct. But they seem to believe that everyone sort of agrees with them already but is prevented from acting on it because of the institutions of government and politics.

That’s wrong. Lots of people honestly, genuinely disagree with Miller and Friedman about this stuff. Many others are indifferent but persuadable.

The problem with the third-party approach is that it’s a magic shortcut and one that (like most magic shortcuts) just doesn’t work. In part, that’s because the U.S. political system just makes it hard for third parties. And in part, it’s because every minute that you spend trying to convince someone to join a third party, and every dollar that you spend on the third party, is a minute and dollar not spent on convincing people that you are correct about your issues.

There’s no guarantee, of course, that even those who go about this sort of thing the right way will ever win. Third-party fantasies, however, are nothing but distractions from the hard work of coalition-building and real persuasion. My suggestion: Find five issues that went from off-the-radar to mainstream over the last couple of decades and figure out what their supporters did. And marriage is an excellent place to begin.