Finally Joe Biden got some good news: He wasn’t the target of his rivals in the party’s fourth presidential debate.

The bad news is that’s because he’s no longer viewed as the front-runner.

That distinction clearly belongs to Elizabeth Warren, as proven by the fact that the target Biden has been wearing was now on her back.

One by one and sometimes in succession, her rivals took aim. And, showing their own relative moderation, nearly all of them did it by charging that Warren’s plans were too big, too expensive and, when it comes to paying for them, too vague.

The only person who got beat up more than she was President Trump. For her part, Warren seemed taken aback, but never lost her cool.

The pounding on her was especially acute over her repeated refusal to say whether her Medicare-for-all plan would result in middle-class tax hikes. Asked directly by a moderator, Warren said, “Let me be clear,” then proceeded to obfuscate, duck and dodge until her time was up.

The exchange was one of several that revealed what the polls have been showing: Biden is slowly sagging and likely faces more trouble over his son’s profiteering from Joe’s days as vice president.

Warren, meanwhile, is growing in strength, both nationally and in the early states. And she stands to benefit the most when Bernie Sanders leaves the race, with his recent heart attack likely ending any long-shot hope he had of winning the nomination.

Indeed, Warren is on such a roll that her rivals spent most of the night trying to poke holes in her momentum.

It was left to Beto O’Rourke to identify what I regard as a key liability of Warren’s campaign, namely her obvious desire to use the power of the presidency to punish rather than help. There’s something stridently negative about that and I’m only surprised that O’Rourke was the one to point it out.

He began the sequence by saying she didn’t seem interested in “lifting people up.” Instead, he said, she is “more interested in being punitive and pitting one part of the country against another.”

Bingo. That insight captures Warren’s finger-wagging demand that everyone “understand” what she knows about the evil nature of corporations, whether it’s Big Oil, Big Pharma, Big Tech, Big Banks or Wall Street.

Her passion never seems to be about the benefits of her plans, only the virtue of singling out wrongdoers for “accountability.”

And anybody who doesn’t agree with her is part of the problem, as she demonstrated when she got little support for a wealth tax. Using sweeping gestures to include her rivals, she accused them of thinking it’s “more important to protect billionaires” than help the middle class.

The harsh spotlight on Warren benefited Biden and may be one of the reasons why he had one of his best debate performances. He seemed more relaxed, and although he still mangled his words and numbers several times, he was passionate about denouncing the slaughter of the Kurds in Syria.

His main calling card is that he “gets things done,” a point he made several times without actually mentioning Barack Obama. It’s not clear if that was deliberate or a slip-of-the-mind mistake.

The evening began with a big fat softball from CNN’s Anderson Cooper. He lobbed an impeachment question and — surprise, surprise — all 12 candidates think Trump is unfit, dishonest, terrible, corrupt, blah blah blah.

Boob bait for the bubbas, as the late Sen. Daniel Patrick Moynihan described such exchanges.

The moment was the highlight for most of the stage, with the top-tier candidates rightly getting the bulk of the speaking time. Despite some complaints to the contrary, the debate proved that the party’s qualifying rules were not strict enough.

The requirement for a 2 percent showing in the polls, which is statistically close to meaningless, meant there were too many candidates and the energy too diffused. It turns out there are good reasons why neither major party ever put as many as 12 candidates on a single stage.

Please, never again.

One consequence is that the debate was not as definitive as it could have been. Of course, it’s still relatively early in the process — the Iowa caucus isn’t until Feb. 3 — but the ideological split is not anywhere close to being resolved because so many candidates give the illusion of many choices.

In fact, it’s a two-person race, but neither Biden nor Warren seems ready to unite the party. And it’s getting close to being too late for a newcomer. Although Michael Bloomberg is said to be sniffing around again and Hillary Clinton is making noises, there is no draft movement for either one of them.

Rather, it’s almost certain Dems will have to make a choice between Biden and Warren. Tuesday night didn’t make the choice easier or more appealing.