WHAT TO WATCH WHEN DEMS DEBATE

The Democratic National Committee assigned the 20 presidential candidates for this week’s debates to the two nights by lot in hopes of avoiding the 2016 Republican bias towards candidates leading the polls. They didn’t totally succeed.

As a result, viewers will see an undercard next Wednesday night that includes only one of the current five top contenders — Sen. Elizabeth Warren — and a main event Thursday with the four others.

Here are some things to watch:

WEDNESDAY NIGHT

› Beto’s big chance. For weeks, former Rep. Beto O’Rourke avoided the national media, concentrating on honing his message and responses at hundreds of town halls in early primary states. That cost him dearly in the polls, mitigating the buzz that greeted his entry into the race.

His performance Wednesday night will show if his strategy was smart. Besides Warren, the former El Paso congressman will be matched against at least three other early season disappointments — Sens. Cory Booker and Amy Klobuchar and former HUD Secretary Julian Castro.

› Julian’s big chance. Even more than O’Rourke, the former San Antonio mayor and housing secretary seems to have disappeared in the vastness of the Democratic field. This may be his last chance to assert himself.

› Mixed blessing for Warren. On one hand, the scheduling cost the Massachusetts senator an opportunity to confront fellow New Englander Bernie Sanders, her main rival for primacy on the Democratic left. On the other, her clarity of expression and focus on specific solutions may enable her to stand out against lesser rivals.

› Best of the rest. It will be interesting to see if Booker, Klobuchar or anyone else challenges Warren, whose national poll numbers have gone up.

THURSDAY NIGHT

All eyes on Biden. As a front-runner under duress, former Vice President Joe Biden will be watched closely for how he responds to expected attacks from some rivals, both on issues and whether he is right for the times.

Sanders and South Bend, Ind., Mayor Pete Buttigieg have already challenged his candidacy as backward-looking. This is their chance to do it in person.

The optics could pose another challenge to Biden: Does he look his 76 years in a field where most candidates are 20 or more years younger? The contrast will be especially striking with Buttigieg, who was born while Biden was serving his second Senate term.

› Challenge to the left. Though Warren won’t be present, you can bet former Colorado Gov. John Hickenlooper will challenge Sanders’ socialism. A Hickenlooper-Sanders clash may spare Biden some grief — but, as the front-runner, he’ll probably get enough anyway.

› Can young be too young? Will the 37-year-old look too young to be considered presidential — or does he provide the perfect contrast to Biden, Sanders and 73-year-old President Donald Trump?

› Can Kamala Harris stop waffling? After a promising start, the California senator’s campaign has plateaued, in part due to her caution in approaching controversial issues and her missteps in answering questions on Medicare for all and voting rights for prisoners.

BOTH NIGHTS

What role will Donald Trump play? Will candidates choose to spend their limited time calling for the president’s impeachment? Will they focus on Biden and other more immediate rivals? Or will they concentrate on selling their own prescriptions for the country?

Post-debate punditry — and subsequent polling — will determine the winners and losers. But the latter shouldn’t fret too much; they’ll get another chance next month.