“Joe picked the right partner in Kamala,” Clinton said. “She’s relentless in the pursuit of justice and equity, and she’s kind … I know something about the slings and arrows she'll face, and believe me this former district attorney and attorney general can handle them all.”

The shape of the Democratic Party’s transformation was pre-ordained with Biden’s selection of Harris as his running mate last week. He is the “transition candidate,” as he once called himself. And she became the instant frontrunner in the party’s next contested primary – whether in 2024 or 2028.

But the transition could have been so much more painful for the party. Somehow, it was Clinton who made it less so.

But it was Harris's night, as she accepted the vice presidential nomination.

Here are some key takeaways from Night 3 of the Democratic National Convention.

Harris matters. Really.

Biden is leading in public opinion polls mostly because his supporters want to get rid of Trump, not because their hearts burn for the Democratic nominee.

That would be fine if the election were tomorrow. But Democrats are eager to more fully define Biden’s candidacy on its own terms ahead of a fall election season in which Republicans will spend enormous sums to drag him down.

Harris helps with that. She's viewed favorably by 54 percent of Americans, versus 29 percent who have a negative opinion, according to recent ABC News/Washington Post poll. A majority views her as qualified to take over for Biden if necessary (a not inconsequential concern, given his age).

Harris also speaks to critical swaths of the electorate in ways that Biden can’t, including younger voters, women and people of color. And on Wednesday, Harris worked to warm those constituencies to her running mate.

“We must elect a president who will bring something different, something better, and do the important work,” she said. “A president who will bring all of us together — Black, White, Latino, Asian, Indigenous — to achieve the future we collectively want. We must elect Joe Biden."

Of course, Harris has bigger plans.

It can be easy to dismiss a vice presidential nominee. Nobody is talking with such certainty about Mike Pence as the future of the Republican Party. Nor did Democrats have high expectations for Tim Kaine. But Harris is different — so much so that one source of uneasiness surrounding her was how loyal she might be to Biden.

On Wednesday, Harris did something to address that. She introduced herself. She was an antagonist to Trump. But the framing was all Biden.

"Right now, we have a president who turns our tragedies into political weapons,” she said, in a line that’s continuation mattered just as much as its start. “Joe will be a president who turns our challenges into purpose."

Biden was watching from Delaware, where the campaign is attempting to keep the focus on Harris.

Hillary, revisited

Hillary Clinton has been a headache for Democrats since losing in 2016, losing a contest decided in large part by voters who liked neither her nor Donald Trump.

And the Democratic Party clearly had no interest in looking back.

“Tonight, we’re going to talk about where we are and where we’re going,” Kerri Washington, the emcee, said at the outset. And if that was too subtle, Billie Eilish sang, “My future.” But Clinton’s endorsement of Biden and Harris was full-throated.

“Yes, it still takes a village,” she said, referencing her 1996 book. “And we need leaders equal to this moment of sacrifice and service. We need Joe Biden and Kamala Harris."

But there also was was a hint of a re-litigation of her 2016 election loss to Trump that many Democrats would rather avoid.

“For four years, people have told me, ‘I didn't realize how dangerous he was. I wish I could do it all over. Or, worst, I should have voted.’”

But public opinion is fluid. Just ask Jimmy Carter. At some point, sharp edges tend to fade. Since Clinton’s loss, women asserted themselves in the midterm elections and, if Trump loses, they will likely be the proximate cause.

In that light, Clinton’s brief, rhetorical return to the last election served as less of a lament than a warning.

“Look,” she said, “this can't be another would have, could have, should have election.”

Now Obama’s the "friend"

It will all change in November if Joe Biden beats Donald Trump. But for now, the Democratic Party is still, in important ways, the party of Barack Obama. For Democrats, no politician can speak with more authority, as Obama did Wednesday, about the custodianship of democracy.

Obama’s stature was clear during the presidential primary, in which Biden — keenly aware of Obama’s lingering glow — mentioned his association with the former president ad nauseum.

It was easy to snicker at the cling-iness then, while Obama was not publicly taking sides in the campaign.

But now he is, and the attachment matters more than ever. Cue Obama on Wednesday calling Biden both a “brother” and a “friend.”

“Twelve years ago, when I began my search for a vice president, I didn’t know I’d end up finding a brother,” Obama said. “Joe and I come from different places, different generations. But what I quickly came to admire about Joe Biden is his resilience, born of too much struggle; his empathy, born of too much grief. Joe’s a man who learned early on to treat every person he meets with respect and dignity, living by the words his parents taught him: 'No one’s better than you, Joe. But you’re better than nobody.'"

Put Obama’s stinging indictment of Trump aside (“Donald Trump hasn’t grown into the job because he can’t,” Obama said). It was the kind of speech that could ensure some of his popularity rubs off on the current, less-thrilling-to-Democrats nominee.

The progressive powerhouse

Step away from Twitter, and there was at least as much — if not slightly more — Democratic excitement about hearing from Elizabeth Warren at this convention than there was for Bernie Sanders and Alexandria Ocasio-Cortez.

And for viewers itching talk of Oklahoma, rigged systems and plans, plans, plans, Warren didn’t disappoint.

“The way I see it, big problems demand big solutions,” Warren said. “I love a good plan, and Joe Biden has some really good plans.”There were signals during Biden’s vice presidential search that Warren might not pursue the presidency again. But she has not ruled it out entirely. If Biden doesn't win in November — or if he does, but Harris stumbles — it’s easy to imagine her giving a run a second look.

At 71, she is younger than both Trump (74) and Biden (77).

And what if the 2020 campaign was her last? Warren may end up proving, more than anyone in this year’s sprawling Democratic primary field, that a politician can have enormous influence on the party from the inside.

Biden has taken economic advice from Warren, and he has adopted some progressive causes she has supported, including on college affordability, bankruptcy and Social Security.

Treasury secretary is a real possibility for Warren. One Democratic Party politician who spoke with Biden advisers during the vice presidential vetting said, “It would be a stroke of genius. It would terrify Wall Street.”