More than 16 months are left before Americans over 18 vote on who should be president, and the Democratic nominee won't become her or his party's candidate officially until July next year. But the 2020 campaign is well under way, and a large field of Democrats are getting ready for two debates to be televised live this Wednesday and Thursday by NBC, MSNBC and Telemundo. A different set of 10 candidates will be on stage in Miami each night from 9-11 p.m. "The debates will be unruly," The Washington Post predicts.

These nine politicians are the top-polling Democrats in the crowded field: Joe Biden (third presidential try), Bernie Sanders (second time), Pete Buttigieg, Elizabeth Warren, Kamala Harris, Beto O'Rourke, Cory Booker, Amy Klobuchar and Julián Castro. To spread them out, a random drawing determined which night five will appear and when the other four get their turns. For the top contenders, it's a chance to build momentum. For the bottom rung, it's a chance to break out.

Each of the Democrats competing to challenge Republican President Donald Trump in November 2020 is likely to get roughly six to eight minutes to speak on the crowded stage. They all know it's vital to deliver a sharp, memorable message quickly. These high-risk, high-reward national appearances are widely expected to thin the field at least a bit. Second-tier hopefuls who fail to earn positive news coverage and social media attention may lose donors, volunteers and staff members. "You get one chance to make a good first impression," says Democratic strategist Mary Ann Walsh. Also on stage will be moderators Lester Holt, Savannah Guthrie, Chuck Todd, Rachel Maddow and José Diaz-Balart

Past candidate says: "The strategy is get your point across, never make more than one or two big points, and don't snipe at somebody without thinking it through because you don’t want to look cranky." -- Howard Dean, ex-governor of Vermont who ran for the Democratic nomination in 2004

Historic first: Three female candidates will be on stage each night, more than have ever been in a presidential campaign debate.

Next debates: July 30 and 31 in Detroit