The experience, credentials and policy positions of the person sitting in the veep hot seat will become increasingly relevant the closer septuagenarians Biden, 77, and Trump, 74, approach the age of 80.
Before they go head to head in November, Ms Harris and Mr Pence will face off on stage in the only vice presidential debate of the campaign on 7 October, slated to be held at the University of Utah in Salk Lake City.
The Trump campaign reportedly views Ms Harris as the pick who “scared them most” going up against Mr Pence in the VP debate.
“They thought she would more than go toe-to-toe with Pence, they thought she could chew him up and spit him out,” MSNBC anchor Nicolle Wallace reported.
The president himself said during a press conference on Tuesday that Harris was his “number one draft pick” for the Democrat ticket before saying he would choose his current VP.
“Well I like vice president Mike Pence much better, he is solid as a rock, he’s been a fantastic vice president, he’s done everything you can do,” Mr Trump said.
“He’s respected by every religious group, whether it’s evangelical, whether it’s any other group they respect Mike Pence. He’s been a great vice president and I will take him over Kamala.”
While they will face off in person in Utah, here is how they compare on paper.
Background and Education
Ms Harris, 55, was born in Oakland California in 1964 to a Jamaican father and Indian mother who had immigrated to the United States.
She attended Howard University before entering law school at the University of California.
Mr Pence, 61, was born in Columbus, Indiana in 1959 to a Korean war veteran father who ran gas stations.
He attended Hanover College in Indiana and Indiana University school of law.
Religion and Family
While Ms Harris considers herself a Baptist, her upbringing included a mix of Hinduism and Christianity. Her Mother Shaymala Gopalan was from Chennai, India, and “Kamala” means “lotus” in Sanskrit.
After her mother’s death, however, Ms Harris spent most of her childhood attending churches in Oakland.
She has invoked the Bible and the teachings of Jesus on the campaign trail, commenting on the parable of the good Samaritan during the Poor People’s Campaign forum in 2019.
She is also married to a Jewish husband, Douglas Emhoff, and is stepmother to his two children, Cole and Ella.
The Evangelical Christian is famously known for how his “born again” faith has influenced his policies on everything from abortion to birth control. He was reportedly raised Catholic before attending a megachurch and ultimately identifying as “a Christian, a conservative, and a Republican — in that order”.
He is married to schoolteacher Karen Pence, and they have three children together, Michael, Charlotte and Audrey.
Ms Harris was elected to the US Senate in 2017 after serving as California’s attorney general 2011, two of the highest state-level offices in the largest state in the country.
Before that, she was elected as district attorney for San Francisco after beginning her career in the Alameda County District Attorney’s Office.
Mr Pence entered the House of Representatives from 2001 until 2013. He rose through the Republican party and became Governor of Indiana in 2013 until he was sworn in as vice president in 2017.
Before entering politics, he hosted a talk radio show, which he described as “Rush Limbaugh on decaf”.
Law and Order
With district attorney and attorney general on her resume, Ms Harris as a long record in law and order that could both help and hinder her campaign. During the Democratic primary, she was criticised for being too hard on non-violent crime.
As a senator, she voted for the First Step Act to reform that retroactively reduced the sentences of non-violent offenders. She was a chief author of the Democratic policing reform bill drafted, but not passed, in the wake of George Floyd’s death that went after qualified immunity laws.
Mr Pence has been pitching the White House’s law and order campaign pledge, telling a group of law enforcement officers in Arizona that they’re not going to defund the police, “not now, not ever” and that they’re going to back the blue with more resources and support.
During his speech, Mr Pence marked the clear line between the Republican and Democrat approach to criminal justice, saying there doesn’t need to be a choice between either supporting law enforcement or supporting African Americans.
Ms Harris’ experience leans into domestic policy while opening her up for criticism of a lack of foreign policy experience, but her supporters will point to her position on the Senate Intelligence Committee as indicative of her national security credentials.
Mr Pence has a full term as vice president under his belt, but even before joining the Trump administration he sat on several committees while serving in Congress, including the Foreign Affairs Judiciary.