From an article on CNN.com today:
".... the 79-year-old Biden, despite wisely sending signals that he will seek reelection in 2024, may decide that he doesn't want to run three years from now. If Biden does run, as an incumbent, he has an advantage. But if he chooses not to, that doesn't mean Democrats are doomed.
A primary campaign between Harris and Buttigieg could pit two key Democratic constituencies against each other: African Americans, particularly African American women, and LGBTQ voters. The impact of that fight would be even worse if it began in 2023 and took over the second half of Biden's current term.
Fortunately, this is a problem that can be easily solved without either politician having to give up anything lasting. Harris and Buttigieg instead could agree that, if Biden does not run again, they would run together in 2024, with Harris the nominee for president and Buttigieg for vice-president. This could put an end to whatever feuding exists between them now, while giving the Democratic Party a very strong ticket in 2024 that would seem like a natural continuation of Biden's first term.
A Harris-Buttigieg ticket would showcase two dynamic politicians and represent the breadth and diversity of the Democratic Party, and indeed the whole country, while not veering too far left and alienating key swing voters who Biden won in 2020. This ticket would be balanced with regards to geography: Harris is unmistakably Californian while Buttigieg is from Indiana, and brings with him a deep understanding of the Midwest.
Harris would be 60 years old on Election Day 2024, while Buttigieg would be 42, so there would be generational balance there as well. Both nominees represent important Democratic Party constituencies -- Harris is an African American and Asian American woman, while Buttigieg is a gay man. This would help mobilize important parts of the Democratic base. However, both politicians are essentially moderates, so it would be hard for the Republican Party to effectively tar them as radicals, socialists or anything like that -- something they would undoubtedly try to do. During, and since, the 2020 election, the right wing has tried to paint Harris as being on the far left, but that attack never got much traction."