Four names are getting the most attention from Joe Biden in the race to be his running mate: Sens. Kamala Harris, Amy Klobuchar, Elizabeth Warren and Gov. Gretchen Whitmer.  Three of those four have begun to attract some degree of open opposition. The only one who hasn’t is Harris. And that makes her the safest choice for vice president.

A fifth name that has generated a lot of media attention is former Georgia state legislative leader Stacey Abrams, because she has been so publicly vocal in advocating for her nomination. However, she has not been a guest on Biden’s podcast, as have Klobuchar and Whitmer. She has not been part of a Biden campaign virtual town hall, as has Harris. And she has not proposed a policy plank that Biden has adopted, as has Warren. Abrams does not appear to be on the short list.

The others almost certainly are, and in turn, have been stepping up their public appearances. That allows both Biden and the rest of us to assess how the public would receive them. It’s not necessarily helping their causes.

“Perhaps no other potential vice-presidential contender has stirred as acidic a reaction in progressive circles as Klobuchar,” reported McClatchy’s David Catanese. The Minnesota senator personifies an electoral argument that the Biden campaign should expend most of its energy appealing to white, moderate Midwesterners, which stirs worry on the left that the interests of people of color and progressive activists will get sidelined. Plus, during the end of her presidential run, Klobuchar struggled to explain her role, while serving as Hennepin County Attorney, in the life sentence of a black teenager convicted of murder on scant evidence.

Back in March, founder Markos Moulitsas summed up, on Twitter, the view of Klobuchar skeptics on the left, arguing she “would be Tim Kaine 2.0—doing nothing to unify the party, bringing no new demographics to the ticket. It would be (once again) a disaster.”

On the flip side, “[b]ig money donors are pressuring Joe Biden to not choose Sen. Elizabeth Warren,” according to a report from CNBC’s Brian Schwartz. One Biden fundraiser is quoted as saying, “I think a lot of the donor base, on board and coming, would prefer almost anyone but Elizabeth.” Warren retains a fervent progressive fan base; a Data for Progress poll of likely Democratic voters found Warren was the plurality choice for vice president with 31%. But as we learned in the primary, consolidating the most progressive third of the Democratic electorate isn’t the same as earning broad party support. Furthermore, the Biden campaign faces a steep fundraising challenge. The Trump campaign is flush with cash, and the virus-ravaged economy will make it hard for Biden to catch up. A vice presidential pick who makes that job harder will likely make Biden pause.

Whitmer, the governor of Michigan, is demographically similar to Klobuchar, and could also deflate those Democrats looking for a nonwhite running mate. But perhaps a bigger problem for her chances is that she has attracted vociferous opposition among Michigan conservatives for her strict social distancing measures in response to the coronavirus outbreak.

You may think upsetting conservatives isn’t a bad thing for a Democratic vice presidential candidate, who often play the role of attack dog. But the supposed value of Whitmer is she would lock down her own swing state with ease. The more she becomes a polarizing figure at home, the less easy that job becomes. Getting mired in local controversies is not what the Biden campaign wants from a running mate.

We already have a bit of data to suggest Whitmer’s rising national profile isn’t helping her vice presidential case, even though her job approval numbers are healthy. A Fox News poll of Michigan shows Biden ahead of Trump by eight points, but when Whitmer is added to the ticket, the lead is trimmed to six.

Which brings us to Kamala Harris. You can make arguments about what she would not bring to the ticket. She’s not from a swing state. She didn’t run a strong presidential primary campaign. She conspicuously used racial issues to attack Biden, who then performed much better than she did with African American voters -- so there’s little reason to assume she would boost African American turnout.

But Harris, at a minimum, fulfills the number one criteria for vice presidents: Do No Harm. Even the best vice presidential candidates rarely flip states, but the worst candidates become distractions that cast doubt on the presidential candidate’s decision-making abilities. As a liberal woman of color, she won’t be subject to complaints from the left. As a mainstream Democrat with a pragmatic streak, Harris can ably work the fundraising circuit. As a senator from the deep blue state of California, she won’t be dogged by home state conservatives (and as a bonus, the odds her Senate seat will get snatched by a Republican are extremely low).

Harris is not without detractors. Some on the left dislike her background as a prosecutor, and repeatedly called her “a cop” during the primary. Some on the right have tried to demean her career by suggesting she was improperly aided by a former boyfriend, former San Francisco Mayor Willie Brown.

But these factions appear to be small. Those on the left who strongly dislike Harris, dislike Biden even more. No vice presidential pick could appease them except for one that risks alienating donors or swing voters, such as Warren (and even Warren might not be enough). And attacking Harris about her past relationship with Brown isn’t universally acceptable on the right. For example, Tomi Lahren was criticized by two of her fellow Fox News personalities last year after she rhetorically asked on Twitter, “[D]id you sleep your way to the top with Willie Brown?” (Lahren soon apologized.)

There is no “Stop Harris” effort afoot, which is important because Joe Biden is running as a unifier, for the country and for his party. A unifier can’t comfortably run alongside a polarizer. Klobuchar, Warren or Whitmer probably wouldn’t become laughingstocks like Sarah Palin or Dan Quayle, or get dumped from the ticket as was George McGovern’s first choice, Thomas Eagleton. But if their selection was greeted with anger by any faction, that would undercut Biden’s persona.

Of the top choices, Harris is the least polarizing, and most compatible with how Biden wants to portray himself. Even their past tension from the primary campaign, when Harris harshly attacked Biden’s position on school busing, works in Harris’ favor, as it furthers the case that Biden is a unifier who works with people with whom he sometimes disagrees.

Of course, a sleeper pick is still possible, such as Sen. Tammy Duckworth, Sen. Tammy Baldwin, or Sen. Catherine Cortez Masto. But these long shots have yet to face the heat of the national spotlight. Eventually, if they get on the short list, they will get that scrutiny along with it. And we will find out if one or more is better positioned than Harris to keep the party unified and allow Biden to retain his appeal to swing voters.

If not, Harris will remain the safe choice.