Martin O'Malley, in Des Moines in February 2016. (Dave Kaup/Reuters)

Moments after Hillary Clinton conceded the presidential election to Donald Trump on Nov. 10, talk in Democratic circles turned to the next presidential election. With Clinton, presumably, out of the mix, and Trump, presumably, very much in it, the race to be the Democratic nominee in three years' time is going to be a humdinger.

And it's already started. The leadership PAC tied to former Maryland governor Martin O'Malley (D) conducted a poll in Iowa this month testing the state of play in the Hawkeye State. The poll, done for the O'Malley super PAC by Public Policy Polling, produced these not terribly surprising results: O'Malley at 18 percent, with Sen. Cory Booker of New Jersey at 17 percent and Minnesota's own Sen. Amy Klobuchar at 11 percent. No other candidate received double-digit support. A third of respondents said they “weren't sure” about their choice.

Those numbers mean roughly nothing. The Iowa caucuses aren't until — at least — January 2020, and asking Iowa Democrats who they might think about maybe supporting doesn't tell us much. At most, the poll is a test of name identification. Given that O'Malley ran for president in 2016 (It happened!), it makes sense that he's near the top.

What's more interesting to me are the potential Democratic candidates that O'Malley's super PAC included — and didn't include — on their ballot test. Aside from O'Malley, Booker and Klobuchar, the other names included in the poll were: former secretary of housing and urban development Julián Castro, New York Gov. Andrew Cuomo, Sens. Kamala Harris of California and Kirsten Gillibrand of New York, Facebook Chief Operating Officer Sheryl Sandberg and Starbucks Chairman Howard Schultz.

That's a group almost as notable for who's not in it as who is. Neither Sen. Bernie Sanders (I-Vt.) nor Sen. Elizabeth Warren (D-Mass.), the two candidates widely regarded as the faces and voices of the liberal left, were included in the poll. Had either been in it, they would have almost certainly had a comfortable lead. And no Deval Patrick, the former governor of Massachusetts. Or Mark Cuban, the owner of the Dallas Mavericks, who emerged in the 2016 campaign as one of the most vocal critics of Trump. Or Tim Kaine, Clinton's 2016 running mate. Or Joe Biden!

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(Note: Yes, I mentioned Biden's name primarily to use that GIF.)

The truth is that not all of these people — those O'Malley included in the polls and those he didn't — will run in 2020. And if history is any guide, some people who aren't mentioned at all right now will run — and might even win.

What the O'Malley poll does do is set the early parameters of what the field might look like. The very early parameters.