The woman former vice president Joe Biden picks as his vice president has a good chance of becoming U.S. president by default when Biden wins the presidency and if Biden were to fall seriously ill or die as a consequence of his very advanced age. Last March during a debate with Sen. Bernie Sanders (I-VT), Biden vowed to name a woman as his vice president.

Biden will be 78 years-old when he takes the oath of office as president in January 2021, the oldest person to hold this august position. While he claims to remain in the pink of health, the COVID-19 pandemic, which doctors agree will return during this year's flu season starting October, means his health will remain constantly under threat. The first vaccine for COVID-19 is expected to be used by 2022.

Biden has long acknowledged his age will be a factor in the race and the importance it puts on his choice for VP. Last week, he said one of the ways to deal with age "is to build a bench -- to build a bench of younger, really qualified people who haven't had the exposure that others have had but are fully capable of being the leaders of the next four, eight, 12, 16 years to run the country."

Democrats and liberals have a plethora of qualified women they say Biden can choose from. CNN picked 10 women last week and they were (from one to 10): California Sen. Kamala Harris, Michigan governor Gretchen Whitmer, Minnesota Sen. Amy Klobuchar, Nevada Sen. Catherine Cortez Masto, Massachusetts Sen. Elizabeth Warren, Illinois Sen. Tammy Duckworth, Wisconsin Sen. Tammy Baldwin,  Florida Rep. Val Demings, Stacey Abrams and New Mexico Gov. Michelle Lujan Grisham.

Of these women, Harris and Klobuchar are emerging as the heavy favorites. Harris remains the prohibitive favorite because of her broad appeal among Democrats. And she's only 55 years old to Biden's 77. She appeals to both moderates and progressives.

CNN ranked Harris number one in its list. So, too, did Business Insider, which called her Biden's best vice presidential option. Harris is African American and Indian American. She's from California, the bluest of Blue States. She also made an unsuccessful run for the party's presidetial nomination.

After Harris dropped out of the race, Biden gushed: "I'm so lucky to have you be a part of this partnership going forward. Working together, we can make a great deal of progress. ... I'm coming for you, kid." 

On the other hand, The New York Post picked Klobuchar as Biden's probable VP pick. It said a Biden campaign insider said Klobuchar "could be No. 1" on Biden's short list. Klobuchar's decision to end her campaign before Super Tuesday allowed Biden to consolidate the moderate wing of the Democratic Party and lay the groundwork for his eventual triumph over Sanders.

One reliable source said Klobuchar has standout "political skills" and remains the favorite of the Democratic Congressional Campaign Committee. Biden hopes her presence on the ticket will help nail down Minnesota, which is a critical swing state.