A campaign with an early start and a multitude of contestants heads into high gear this week with a complicated set of debates. And while the contenders struggled mightily to qualify for these events, they will struggle even more to make their voices and their views clear in sessions with nine rivals also grasping and gasping for air time.

There’s nothing conventional about this Democratic campaign — indeed, there’s nothing conventional about their opponent, President Donald J. Trump — so it isn’t surprising that there will be nothing conventional about these debates. The fight cards were chosen by a lottery system so complex that it could only have been conjured up by Democrats, who over the decades have tended to debate rules better than they debate their opponents. The result: There is little method to the madness that begins Wednesday and continues Thursday.

Even so, the lineups present some intriguing possibilities for conflict; the 20 candidates on the stage — and the lonely three who didn’t qualify, Rep. Seth Moulton of Massachusetts, Gov. Steve Bullock of Montana and Mayor Wayne Messam of Miramar, Florida — know that their own survival requires others to be eliminated, the sooner the better.

Here are some possibilities for illuminating exchanges:

— Sen. Bernie Sanders of Vermont v. former Vice President Joseph R. Biden Jr. of Delaware (Thursday). This is the prize fight of the week: two old guys (one grumpy, the other goofy), two men at the top of the Democratic polls, two political figures who have nothing in common except perhaps being members of the human race. Sanders has contempt for the brand of mainstream collegial politics that Biden practices, and Biden is wary of the firebrand left-leaning impulses of his democratic-socialist opponent. The two overlapped in the Senate for two years. They were not boon companions.

— Sen. Amy Klobuchar of Minnesota v. Sen. Cory Booker of New Jersey (Wednesday). These two ordinarily are on the same side in the Capitol, but Senate politics and presidential politics are two different sports — much like Canadian football and the NFL, only more violent. Both are tough competitors with strong prospects in Iowa, which is where the contest between the two will first play out next February. Booker already has a formidable ground game for the state’s frosty caucus night, and Klobuchar is from a state that borders Iowa so has the capacity of importing scores of campaign volunteers. Both will not emerge from the Iowa caucuses with campaigns intact. Their first skirmish is this week.

— Mayor Pete Buttigieg of South Bend, Indiana, v. Sen. Michael Bennet of Colorado (Thursday). Buttigieg is a Harvard graduate and Rhodes Scholar; Bennet was editor in chief of the Yale Law Journal. This is the intellectual heavyweight matchup, perhaps the greatest of all time. Neither is a conventional presidential candidate, but each has ardent supporters and a nimble mind. Bennet is far less well known and will hope to use the debate stage to highlight his cerebral but approachable profile. Buttigieg must use this opportunity to put some policy meat on his popularity bones.

— Rep. Tulsi Gabbard of Hawaii v. Rep. Tim Ryan of Ohio (Wednesday). Both portray themselves as rebels, Gabbard against conventional American foreign policy, Ryan against the political establishment. The truth that dare not speak its name is that hardly anyone has heard of either one of them, and the secondary truth is that they both cannot survive the vicious fight for funds and attention. If one of them can knock out the other, the survivor might win some breathing room.

— Sen. Kamala Harris of California v. Sen. Kirsten Gillibrand of New York (Thursday). Both had moderate records and moved leftward, both had impressive campaign starts, and both have struggled for oxygen as the campaign has developed. It is unlikely that both will survive Iowa and the New Hampshire primary eight days later, so each would like a knockout punch. This week’s debate provides an early opportunity.

— Sen. Elizabeth Warren of Massachusetts v. the other nine (Wednesday). In some ways, Warren is the big winner from the Democratic lottery. She drew the least competitive debate field and, by happy coincidence, probably will be the most polished debater on the stage, with an answer (usually five or six bullet points) and a proposal (white papers for a campaign for the White House) that has never seen an equal in all of American presidential politics.

— Former Rep. John Delaney of Maryland v. Rep. Eric Swalwell of California (inter-league play). Delaney is on the Wednesday card, Swalwell is on Thursday’s. But they make for an intriguing pair. Delaney has been campaigning (without much notice) for two years and has visited all 99 of Iowa’s far-flung counties. Swalwell has been campaigning for less than three months but actually was born in Iowa. Both are earnest, serious and probably doomed. But both have bet everything on the Iowa caucuses. They had better hope there is no television blackout in Iowa this week.

— The remainder men. The three left behind won’t be in Miami this week, but they also will not have to worry about being bullied, interrupted or embarrassed. Moulton was 14 when a former senator from his state, Paul E. Tsongas, had about the same level of support at this point in the 1992 Democratic nomination fight. A cancer survivor, Tsongas defeated Gov. Bill Clinton of Arkansas in the New Hampshire primary. All is not lost for these three left-outs, though little likely will be won.

David M. Shribman is the former executive editor of the Pittsburgh Post-Gazette.