Just like Biden, who was ahead in the polls the entire primary but struggled to look like a winner, Kamala Harris was number one in the veepstakes practically since Biden’s nomination seemed clear, but she also struggled to look like the clear choice, until it turned out that the person everybody thought was gonna get picked all along ended up being chosen. Ever since 2016, it seems like a lot of people are hesitating to believe that what seems most likely to happen will actually happen.
What Biden gets in Harris is a strong debater who may be able to get under Trump’s skin. We saw that in the early primary debates. Her past as a prosecutor and California Attorney General will appeal to those of a more moderate inclination, and this is likely to have contributed to her selection as Biden probably feels he has shored up enough of the progressive wing through his work with Bernie Sanders.
And with as big a lead as he has, he probably didn’t want to take any chances that late in the race by announcing an unknown candidate. Rep. Karen Bass had a lot of the congressional Democratic Party behind her, but she's unknown nationally.
With Kamala, Biden already knows what he’s getting after her run for President and after her time in the Senate. Some people close to Biden held grudges against Harris since her attacks on Biden last summer, but Biden himself was never one to hold a grudge. Time also solves a lot of problems of that kind.
Harris was lambasted for being “too ambitious” to be a part of a transitional Biden administration, but this has long been a sexist smear lobbed at women who dare to do anything at all. Some have said that Harris may turn off voters who are displeased with her prosecutorial record, but most voters are much more motivated by dislike of the opposition than anything else, especially now.
VP picks rarely have any larger electoral effects, LBJ won Texas and other southern states for Kennedy in 1960, but that is a pretty lonely example. It’s not like Biden wasn’t gonna win California had he not picked Harris. It’s worth remembering in this time of firsts, Harris is not only the first black woman but also the first person of South Asian descent, her mother having immigrated from India in 1960, to appear on a major party presidential ticket.