Joe Biden’s closing message to the American electorate is a vain hope, something we’d like to believe but know in our hearts is impossible. But he should keep saying it, because the alternative is worse.

That message is summed up in this ad:

“This is our opportunity to leave the dark, angry politics of the last four years behind us,” Biden says. “To choose hope over fear, unity over division, science over fiction. I believe it’s time to unite the country, to come together as a nation.”

If only it could be so.

Biden has been talking this way from the beginning of his campaign, expressing his faith that with the right leadership and commitment, America can unite in common purpose. He says this in reference to the broad divisions in the country, and also insists that collectively we are better than the moral squalor of the Trump era. He’ll note some specific outrage — President Trump separating children from their parents, or giving a shout-out to white supremacists — then say, “This is not who we are.”

The trouble is, it is who we are, or at least it’s who lots of us are. That was the whole theory behind Trump’s presidential candidacy in 2016: We are resentful, fearful and hateful, and we want someone who will not only give voice to those emotions but also give us permission to express them as loudly as possible.

In this Trump was the exception, not the rule; Biden’s promise of unity is notable now only because it contrasts so starkly with his opponent. Presidential candidates pledging to bring the country together is so common that before now it was just what we’ve come to expect.

It’s what Bill Clinton said 28 years ago in his convention speech:

For too long politicians have told the most of us that are doing all right that what’s really wrong with America is the rest of us. Them. Them, the minorities. Them, the liberals. Them, the poor. Them, the homeless. Them, the people with disabilities. Them, the gays. We’ve gotten to where we’ve nearly themed ourselves to death. Them and them and them. But this is America. There is no them; there’s only us.

Then eight years later, George W. Bush said in his convention speech that he could lead us out of the partisan morass:

I don’t have enemies to fight. I have no stake in the bitter arguments of the last few years. I want to change the tone of Washington to one of civility and respect.

Then eight years after that, Barack Obama insisted in his convention speech that we all shared a common patriotism and a common destiny:

The men and women who serve in our battlefields may be Democrats and Republicans and independents, but they have fought together and bled together and some died together under the same proud flag. They have not served a red America or a blue America — they have served the United States of America.

Every time, the people voting for those candidates thought they might deliver us to that gentler politics, and every time they were wrong.

Part of it was the partisan sorting that made both parties more ideologically and demographically different from each other with each passing year. And part of it was the decisions of individual actors. One thing the Obama years in particular demonstrated was that if one side seeks bipartisanship and the other side seeks division, the dividers win.

That was Mitch McConnell’s theory of opposition, one he wasn’t afraid to say out loud. While the Obama administration spent months trying to persuade Republicans to work with it on the Affordable Care Act, McConnell told the New York Times that denying Obama bipartisan support was his express goal.

“If the proponents of the bill were able to say it was bipartisan, it tended to convey to the public that this is O.K., they must have figured it out,” McConnell said. Withholding any and all Republican support would demonstrate to voters that Obama had failed as a unifier, which McConnell saw as necessary to Republicans retaking power.

And of course, then came Donald Trump, with his unfailing radar for what is worst in people and conviction that feeding it is the only route to his success.

Even if Biden beats him, the Trumpist style will pervade Republican politics for some time to come, as other ambitious politicians try to use it themselves. But there’s also a more substantive reason that unity will be so hard to achieve.

There may be times in the next four years when the parties agree on a piece of legislation or two, but on the most important issues there simply will be no common ground. That’s not only because Republicans will once again find political advantage in doing everything possible to make a President Biden fail, but also because the parties have profound differences about both ends and means.

Democrats want more people to have health insurance, especially through the government; Republicans want fewer people to have it. Democrats want to enhance workers’ rights; Republicans want to limit them. Democrats want to raise taxes on the wealthy; Republicans want to cut them. Democrats want to move aggressively to limit climate change; Republicans don’t. Democrats want to secure abortion rights; Republicans want to eliminate them.

These are not bridgeable gaps. There isn’t a compromise waiting to be found if everyone just rolls up their sleeves, uses their common sense and hashes things out. Which means that the policy fights will be intense, and one side will win while the other side loses.

Where does that leave someone like Biden, who sincerely wants to bring the country together? His only real choice is to keep saying it, even if he knows that he, too, will fail.

So many of us want to believe it’s possible, even if we know in our hearts it isn’t. More importantly, the president should keep telling us that we are one nation. Because the alternative is something like Trump, turning every disagreement into poison and encouraging strife, anger and ultimately perhaps violence.

The choice is not between unity and division. It’s between a division we will lament but tolerate, and one so intense it rips the country apart. If Biden can give us the former and help to keep us from the latter, it will be more than enough.

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