Joe Biden is set to enter the presidential race. (Michael Dwyer/AP)
Opinion writer

Thirty-two years after he first ran for president — and without a day in between when he didn’t pine for the Oval Office — Joe Biden is ready to take one last shot:

Former vice president Joe Biden is planning to enter the 2020 presidential race on Thursday, nearly finalizing the crowded field of Democrats with a candidacy that will test many of the questions coursing through the party.

Biden is expected to make the announcement in a video, according to a source close to him, which will be followed by a trip Monday to a union hall in Pittsburgh.

One of the first events for the campaign will be a high-dollar fundraiser Thursday night, sponsored by a group of supporters including Comcast senior executive vice president David L. Cohen. Biden over the next week or so is expected to travel to Iowa, New Hampshire and South Carolina.

Perhaps on Thursday, the former vice president will answer the key question confronting him: Why Biden?

Regular readers will know that this is a question I've been encouraging the candidates to address: not just what their strengths and weaknesses are (though those questions are important), but what the central rationale for each of their candidacies is. Why are they running for president? What do they hope to achieve in office? How would the government and the country be different if they're successful?

For every ambitious politician, a good part of the true and unspoken answer is that they want to be president because they want to be president. That's particularly true for Biden, who to his credit has never hid his ambition and has watched over and over as people he probably considered less worthy than himself got the Democratic nomination.

But now there’s a real sense that the time for a Democrat like Biden may have passed, and not just because he’ll turn 78 shortly after the election. Biden is not only a moderate in a party that has moved to the left; he also values negotiation and compromise, and believes that through his relationships with Republicans and his persuasive abilities, he’ll be able to forge bipartisan agreement.

When the other candidates reject that idea, it isn’t because they’re just more combative than he is. It’s because they’ve watched the GOP over the past decade. Biden should know this well, since he was vice president when congressional Republicans decided that their best strategy would be to refuse to work with Barack Obama on anything.

Every major accomplishment of Obama's presidency — the stimulus, the Affordable Care Act, the Dodd-Frank reform of Wall Street — passed with either zero Republican votes or just a few. Obama made endless attempts to compromise with Republicans, and they all failed.

Today's GOP is even more conservative and even more intransigent than it was then. If Biden has reason to believe they'd work with him to advance progressive legislation, it'll be interesting to hear what it is. We don't yet know if "I'm the one who can achieve bipartisan compromise" will be a central rationale for his candidacy, but if it is, he's going to be greeted with a lot of skepticism.

That’s not to say he doesn’t have an overall case to make. He can argue that he has more experience in the federal government and the executive branch than any other candidate, which he does. In a different era, that would have meant more than it does now. He can say that his long time in government gives him a unique ability to perform the administrative tasks of the job, but he’ll have to explain why that should be more important to primary voters than, say, a more progressive agenda.

There are also hints that Biden's campaign will be old-school. As Politico recently reported, his strategy is "to solidify his front-runner status with a wave of high-profile organizing, fundraising and endorsement news when he enters the race." In other words, he'll try to impress observers (especially in the media) with an initial show of strength in the kind of traditional metrics we've used in the past to evaluate campaigns.

As Ed Kilgore notes, that sounds a lot like the “shock and awe” strategy used four years ago by Jeb Bush, who did indeed raise lots of money and get lots of endorsements. You’ll remember how that turned out.

On the other hand, we can easily forget that there’s a significant portion of the Democratic electorate that is more moderate and older than the median Democrat. Their presence may be as much of a reason that Biden has led in early polls as simple name recognition.

But I’m guessing that he will spend a good deal of his time making a case that he’s best able to beat President Trump, which is indeed of paramount importance to Democrats. His theory is that there is a large population of Trump voters who, with the proper courtship and the right candidate, could be persuaded to vote for a Democrat. The competing theory is that what this increasingly diverse party needs to do is energize its own voters, particularly the young and people of color, to get to the polls the way they did in 2018. The advocates of that theory argue that it isn’t so much a question of “writing off” Trump voters as not counting on them to deliver you to victory.

Unlike with some of the other candidates (I’m looking at you, Beto), it isn’t hard to imagine Biden as president. But at this stage, what is hard to imagine is what that presidency is supposed to do for us. At the end of eight Biden years, will we have more to show for it than knowing things would have been worse had there been a Republican in office? Will he just be a caretaker, or will he try to do something transformative? Will America be different, and better? If so, how?

All the candidates have to answer those questions, but for Biden they’re particularly acute. In the past he might have been able to say, “Hey, you know me — I’m your Uncle Joe!” But in 2020, that won’t be enough.

Read more:

David Von Drehle: Biden’s campaign might start a lot like how ‘Butch Cassidy and the Sundance Kid’ ends

Jennifer Rubin: Joe Biden gets ready to take the plunge

E.J. Dionne Jr.: A Biden run would be good for the country. It could be hell for Biden.

Elizabeth Bruenig: Is Joe Biden worth it?

Karen Tumulty: Joe Biden’s rustiness is showing