President Biden’s historic but not-so-shocking choice to end his re-election campaign has upended the presidential race. Whether it helps the Democrats depends entirely on what they do now.

Biden’s decision to endorse Vice President Kamala Harris to succeed him may forestall the open convention many hope for. Technically Biden’s decision frees his delegates to vote their consciences. In practice, every delegate who had been pledged to Biden was vetted or selected by his campaign.

What to know about President Biden's decision to drop out of the 2024 presidential race:

• President Biden announced Sunday he is dropping out of the 2024 presidential race — after weeks of prominent Democrats and donors calling on him to withdraw following his disastrous performance in the first presidential debate.
• In a letter posted on X Sunday afternoon, Biden admitted that it is in the “best interest of my party and country” for him to step down as the Democratic nominee.
• Biden wrote that he intends to serve out the remainder of his term and will address the country on his decision later this week.
• In a follow-up X post, Biden endorsed Vice President Kamala Harris for the suddenly open Democratic nomination. “Today I want to offer my full support and endorsement for Kamala to be the nominee of our party this year,” the president wrote.
• Former President Donald Trump reacted to the news by labeling Biden the “worst president in the history of our country” in a call with CNN.

Some will be party activists, but most will be Biden loyalists. It’s easiest for them to do what Biden asks and simply promote his understudy to the starring role.

That choice likely won’t be unanimous. Someone will surely want to challenge her, but it’s not likely to be someone with a strong base in the party. Anyone with national ambitions will know that they won’t get a second shot if they challenge Harris because party animosity will be sky high.

That leaves second raters or people who would want to use a challenge to propel them into the spotlight. Some progressive who thinks Harris is too conservative might get a couple hundred delegate votes, but that won’t trouble her or the national establishment that’s engineered her ascent.

The worst-case scenario for Harris would be an emerging serious challenge she beats off only because of her insider support. That would show even Democratic activists have serious issues with her while also demonstrating she lacks the political skills to halt such an effort in its tracks.

Harris will need to do a lot of work herself, though, to make her nomination meaningful even if she gets it easily. Polls have long shown her favorability ratings are roughly the same as Biden’s. Polls taken in recent weeks have shown she doesn’t run much better against former President Donald Trump than Biden did.

She’s also got a fair bit of baggage herself. Her own verbal tics have become comic fodder on the Internet, and she can’t become an orator overnight. Harris was given responsibility for the border years ago, making her the face of an incredibly unpopular set of policies.

She also has the burden of carrying all of Biden’s unpopular policies. The “Biden-Harris administration” is a blessing in the nomination context but a curse in the general election.

Nor has she ever shown she’s a strong candidate. Her own bid for the 2020 nomination flopped spectacularly as she seemed woefully out of her depth and uncertain as to what she believed. Running against Trump helps her in one respect as all she needs to do is endorse mainstream Democratic beliefs. But she still must convince Americans she has the gravitas and strength to lead.

Harris could make her own mark off the bat by naming a well-known Democratic moderate as her running mate. Men like Sens. Mark Kelly (Arizona) or Gov. Roy Cooper (North Carolina), Josh Shapiro (Pennsylvania) or Jared Polis (Colorado) would be offered as proof moderates are welcome in the Democratic Party. They could also match up well with 39-year-old J.D. Vance, as any one of them would likely claim their experience makes them a better fit for vice president.

She will likely also try to make abortion rights the major issue of the campaign. Democrats have been hammering away on that for months, to little avail, but having a woman make that case might make a difference.

Harris’ bigger challenge will be to persuade the black and Latino voters who’ve been abandoning Biden in droves to come home. She’s never shown a lot of strength with black voters — if she had, she rather than Biden would probably have emerged as the alternative to Bernie Sanders in 2020.

But things could be different with her in the ticket’s top position. Latino voters could also find an energetic 59-year-old preferable to the feeble Biden.

Biden’s apparent decision to finish his term, however, could prove an anchor around Harris’ ankles. Vice President Hubert Humphrey found that to be true when he became the Democratic nominee in 1968 after his boss, President Lyndon Johnson, abandoned his campaign.

Humphrey needed to distinguish himself from LBJ’s policies, especially on the Vietnam War, but he could not do so without Johnson changing those policies himself. Johnson refused to do so until just days before Election Day, too late to give his veep the time to reap the benefits.

Nothing should be assumed in this most topsy-turvy of campaigns. Who knows what “unknown unknown,” to use former Defense Secretary Donald Rumsfeld’s memorable phrase, will occur? In the meantime, we should expect the unexpected, but Trump remains a slight but real favorite to win.

Henry Olsen, a political analyst and commentator, is a senior fellow at the Ethics and Public Policy Center.