Jason Sattler

Opinion columnist

All 12 leading Democratic candidates for president got a chance to demonstrate why they were able to meet the requirements to pack on the stage for the fourth debate Tuesday.

Sen. Elizabeth Warren of Massachusetts stayed feisty and focused in her new role as front-runner.

Former Vice President Joe Biden was optimistic and self-congratulatory as he tried to win the John McCain name-dropping contest. Rep. Tulsi Gabbard of Hawaii confounded everyone by spreading the blame for the slaughter of the Kurds in northern Syria that Donald Trump invited to members of “both parties.” And Andrew Yang got to say lots of things as if no one had ever thought of them before.

But the winner of the night was older than the two youngest candidates on stage — Gabbard, 38, and South Bend, Indiana, Mayor Pete Buttigieg, 37 — combined.

Vermont Sen. Bernie Sanders, 78, returned to the campaign trail after recovering from a heart attack to deliver his strongest debate performance of the campaign. He was lively, funny and persuasive. At one point, he even seemed to convince billionaire Tom Steyer that billionaires shouldn’t exist.

Sanders also took on Biden’s constant praise of bipartisanship and his pointed boast, “I'm the only one on this stage that has gotten anything really big done.”

“Joe, you talked about working with Republicans and getting things done,” Sanders said. “But you know what you also got done — and I say this as a good friend — you got the disastrous war in Iraq done. You got a bankruptcy bill, which is hurting middle-class families all over this country. You got trade agreements like NAFTA and PNTR (permanent normal trade relations) with China done, which have cost us 4 million jobs. Now, let's get to 'Medicare for All.' ... If we stood together, we could create the greatest health care system in the world.”

A conservative's take:Winners and losers in the Democratic debate from columnist Glenn Harlan Reynolds

But Bernie’s biggest moment of the night didn’t happen onstage. In the closing minutes of the debate, news broke that one of the brightest young stars on America’s left, Rep. Alexandria Ocasio-Cortez of New York, will endorse the 2016 Democratic primary runner-up this weekend.

This gives the democratic socialist from Vermont the chance to break the momentum of Warren’s steady rise in the polls, though he notably hasn’t taken a shot at the senator from Massachusetts on the debate stage yet. Instead, he sided with her several times as she was cornered, echoing her arguments for systemic change.

The format of the debate flowed much better than the previous three. It’s unclear whether this was because the moderators allowed the candidates more air to answer and rebut each other, or because self-help guru Marianne Williamson wasn’t on the stage. Whatever it is, they should do more of it.

While there are still miles to go before anyone actually votes for a nominee, the race for the chance to oppose Trump will likely remain a tossup among Sanders, Warren and Biden. This is mostly because the rest of the candidates have done a better job of canceling each other out than breaking through.

While the debates have led to some blips in the polls — most notably for Sen. Kamala Harris of California after the second debate — the crowded stage format has the effect of blurring candidates together, especially since every debate seems to rehash the same Medicare for All contentions over and over until even Sanders seems a little bored by the fray.

Another huge winner of the night was impeachment, which is now polling 50%.

Every candidate on stage backs the inquiry in the House, and no candidate showed any willingness to echo the attacks on Hunter Biden that Trump pressured Ukrainian President Volodymyr Zelensky into trumping up.

Unfortunately, the biggest loser of the night was human civilization.

While there was a question about Ellen DeGeneres’ defense of her kindness to former president and torture purveyor George W. Bush, there wasn’t one question about climate change. Future generations will have to be satisfied knowing that we were much too busy worrying about rich people getting along in luxury boxes to stop the planet from boiling.

Jason Sattler, a writer based in Ann Arbor, Michigan, is a member of USA TODAY’s Board of Contributors and host of "The GOTMFV Show" podcast. Follow him on Twitter: @LOLGOP