The Biden Eclipse and the Trump Plateau Hillary Clinton pre-empts her biggest challenge as Republicans consider their alternatives.

Something big happened at the Democratic debate. It didn’t have to do with Hillary Clinton besting Bernie Sanders or Jim Webb. What she had to do, after the long, battering summer, was show she is up to the battle, ready for it, capable—that she can do this. She did. She was crisp, lively, a presence. In demonstrating that she is up to the race she deprived Vice President Joe Biden of his rationale for getting into it. People say he didn’t have a rationale but of course he did, it just wasn’t something he could say or leak. His rationale, at 72 and having recently experienced great loss, was: The party’s in trouble, the front-runner can’t win, she’s too encrusted by scandal, in an act of heroic sacrifice I’m going to swoop in and save the day.

But she had to tank, and very obviously, for him to swoop. She didn’t. If she had, I suspect we’d be spending the weekend hearing about his impending candidacy. We won’t.

I don’t see how he gets in now.

Vice President Joe Biden

Vice President Joe Biden

Too bad! Mr. Biden would have added a layer of affection to a so-far cold enterprise. He would have added an element of old-time normality to the field. He would have been as entertaining in his way as Donald Trump, and it would have been instructive to see how Democrats respond to the entrance of President Obama’s two-term vice president. Who has the party’s heart?

It would have been great. But if he jumped in now he’d look like a spoiler, doing it not to save the party but fulfill his sense of destiny. He won’t want to look that way. If he were willing to look that way he would have announced six months ago.

Luck matters in politics as in life and Mrs. Clinton has now been lucky twice in a short time. Kevin McCarthy blunted Republican arrows on Benghazi, then Bernie Sanders blunted arrows by saying the email scandal doesn’t matter. To many of his supporters, presumably, it did. Now all Democrats have permission not to care. It’s nice to get a pass like that!

And now the one candidate who could have derailed her will likely not get in. She is on a roll.

The Democratic debate revealed two other things. The 2008 Democratic contest was a rush to the center, with both leading Democrats, Mrs. Clinton and Barack Obama, trying to show they were moderates at heart. The 2016 primary is a rush to the left. We are now not embarrassed to argue America should be more like Denmark, we are proudly socialist or severely progressive, and by the way Republicans are the enemy. Asked which enemy she was proudest to have made, Mrs. Clinton mentioned the NRA, the Iranians, some others and “probably the Republicans.” She was smiling, but if any GOP hopeful declared “the Democrats” to be on his enemies list he would be roundly condemned as polarizing, and people like me would be saying: “You don’t demonize the other team, you win them over!” It is interesting that in Mrs. Clinton’s case that isn’t happening.

If the Democratic candidates are rushing to the left it’s because they know some significant quadrant of the base is there. If Hillary feels free to speak of the Republicans as enemies it’s because she knows there is a portion of the base that is angry, polarized and ready to respond to an aggressive tone.

We hear a great deal about uncompromising anger on the Republican side and none about the take-no-prisoners resentment on the Democratic side. But it’s there.

Which gets us to Donald Trump, who had another good week with smashing polls in Connecticut, Nevada, South Carolina and Virginia. ( Robert Costa of the Washington Post says the untold story now is Mr. Trump’s state organizing.) But the smartest new data I saw this week was from Target Point, which conducted a national poll of likely Republican primary voters from Sept. 29 through Oct. 1. I call it smart because it confirms my own observations and biases.

It found the GOP electorate to be “extremely fluid.” No candidate is close to a majority. The average respondent is still considering six different candidates. Twenty-nine percent of those polled didn’t express a clear preference for any one candidate. Most are trying to choose between two favorites. Those enjoying increased consideration are Ben Carson, Chris Christie, Carly Fiorina and Marco Rubio.

Mr. Trump, according to Target Point, is not slumping. But “he does appear to have plateaued.”

That’s what I’m seeing too. Talking to Trump supporters this week I’m getting a sense of stalling or slight deflation. The early thrill is gone. No one mentions that it’s something he said or did. I get the impression some supporters are saying: “It’s not you, it’s me.” They’re wondering if they themselves will continue to feel the early electrical charge of Mr. Trump. They’re wondering if they will find another candidate they like as much or more. They’re not sure. A relative and early Trump enthusiast said Wednesday on the phone, “He’s—he’s not going to go in there and say, ‘I’ll bomb someone,’ right? I mean he’ll have the regular professional generals and all the military people surrounding him, giving him advice—right?” I could hear a certain wavering. But then he stopped talking because he didn’t want to wind up in a column.

Mr. Trump announced in June and has been in the lead through now mid-October, and every political sophisticate I know continues to be gobsmacked at what it all means and portends.

I have been seeing my friends go through the five stages of Trump, which are like the Kübler-Ross stages of grief. The first is denial (“He’s going nowhere, he’s a farce”). Second is anger (“This vulgar slob of a fool has some nerve messing with the American electoral process for his own enjoyment”). Next, bargaining (“If we make him promise to support the party if he doesn’t win, and he refuses, won’t that ruin him with the base?”). Then depression (“He’s a reality-TV star! He has the hair of an abnormal person! He’s our next president? I must have picked the wrong year to give up hallucinogens”). And finally acceptance (“We’ve had worse”—a Democratic political professional actually said that to me).

The only thing I feel certain of is how we got here. There are many reasons we’re at this moment, but the essential political one is this: Mr. Obama lowered the bar. He was a literal unknown, an obscure former state legislator who hadn’t completed his single term as U.S. senator, but he was charismatic, canny, compelling. He came from nowhere and won it all twice. All previously prevailing standards, all usual expectations, were thrown out the window.

Anyone can run for president now, and in the future anyone will. In 2020 and 2024 we’ll look back on 2016 as the sober good ol’ days. “At least Trump had business experience. He wasn’t just a rock star! He wasn’t just a cable talk-show host!”