Joe Biden's entrance into the 2020 presidential race is a seismic shift, here are the rival contenders that are in the most trouble

Lots of campaigns will have to contend with Biden's entrance in the race. Still, based on our polling, four candidates in particular are trying to primarily reach constituencies that like Biden a lot more than the typical Democrat we surveyed.

Overall, 63% of Democratic primary voters we surveyed would be happy with Biden as nominee.

• Among the surveyed Democrats who'd be happy with Sen. Kirstin Gillibrand as nominee, 69% also would be satisfied with Biden, a figure that is 6 points higher than a typical Democrat.
• Of those who would be happy with Sen. Amy Klobuchar as nominee, 70% like Biden.
• Looking at those who'd be satisfied with Beto O'Rourke as nominee, that figure jumps to 71%, an 8 point bump in Biden fans over the baseline.
• 72% of people who'd be satisfied with Sen. Cory Booker as nominee would also be satisfied with Biden, 9 points higher than the typical Democrat.

The candidates that suffer the most from a Biden entrance are those who overlap the most in constituencies and who are not sure-footed enough in the campaign to guarantee a strong base of voters by the time people head to the polls. Besides O'Rourke, none of these candidates have cracked 5% in Morning Consult's tracker.

There's no guarantees, but if Biden's making a dent on the field one of these four candidacies will likely be the first to show it.

Next we come to the campaigns of Sen. Kamala Harris and Sen. Elizabeth Warren. Biden's entrance is actually a little bit more complicated for these candidacies, because while the former VP's presence in the race presents medium-term challenges, there may actually be some short-term benefits.

Essentially, the four candidates specifically threatened by Biden also have supporters who really like the Warren and Harris candidacies, meaning that if Biden's entrance causes one or more of the most vulnerable candidates to bow out of the race, Harris and Warren are best poised to pick up those voters.

Compared to the whole set, the senators from California and Massachusetts outperform among those candidates immediately threatened by Biden, in every single case doing better — often by double digits — than their overall performance among Democrats. Their margins are really good among:

• O'Rourke supporters (Harris +5 points, Warren +6 points)
• Booker supporters (Harris +14 points and Warren +10 points)
• Klobuchar supporters (Harris +20 points, Warren +13 points)
• Gillibrand supporters (Harris +22 points, Warren +22 points).

A well-orchestrated Biden campaign does pose a major threat, but the Harris and Warren campaign's strong footing means that his entrance isn't immediately troubling.

Biden is a very immediate problem for lots of campaigns, but he's probably not going to matter until the eve of the Iowa caucuses for these two. In the event Biden were to leave the race, Warren and Harris could stand to gain since the pair are also satisfactory nominees for Biden's fans.

A few campaigns seem fairly insulated from Biden's entrance.

• Sen. Bernie Sanders and Biden will likely be locked in a tough fight, but their perceived electability and presidential track records grants them constituencies that overlap more than you might think: 61% of Bernie supporters would also be satisfied with Biden and 52% of Biden supporters would also be satisfied with Bernie as nominee. If anything, their fates are intertwined: should someone emerge from the field as supremely electable, each campaign may lose their perception advantage and suffer despite their differences.
• South Bend Mayor Pete Buttigieg's supporters don't love Biden the same way Beto, Booker, Klobuchar and Gillibrand's constituencies do. Of those who'd be satisfied with Mayor Pete as nominee, 64% would also be satisfied with Biden, barely a point higher than Biden's performance generally.
• That same logic goes for Former HUD Secretary Julian Castro. Castro's supporters seriously overlap with Sen. Harris and Sen. Booker, both candidates more threatened than Biden than Castro is. His supporters like Biden only slightly more than Democrats generally.

They're both still quite niche and the sample size isn't as robust as the other candidacies already discussed, but those respondents who'd be satisfied with either Rep. Tulsi Gabbard as nominee or businessman Andrew Yang as nominee were less likely to also support Biden than your typical Democrat.

Less than 55% of Yang supporters also would be satisfied with Biden, a 9 percentage point deficit from the baseline Democrat, and only 56% of Gabbard supporters also liked Biden, a 7-point deficit.

The last kind of candidacy threatened by Biden is the one that's so starved for attention that regardless of their overlap or distinctions Biden's entrance in the race sucks enough oxygen out of the room that they're imperiled. This includes:

• Gov. John Hickenlooper and Gov. Jay Inslee, both of whom have bases that like Biden more than your typical Democrat. Two-thirds of Hickenlooper fans and 70% of Inslee backers also would be happy with Biden as nominee.
• Rep. Tim Ryan, Rep. John Delaney, Marianne Williamson, Sen. Michael Bennet, Gov. Steve Bullock and Rep. Seth Moulton, all of whom have not resonated in the race.

With Biden in, the last remaining puzzle piece for the Democratic primary is in place. The immediate effects of a popular front-runner formally declaring will test all the other campaigns, and some of them likely won't be able to withstand that test.