WASHINGTON • Four years ago, Senator Cory Booker of New Jersey made his vice-presidential pitch to Mrs Hillary Clinton at her Washington home, months before she faced Mr Donald Trump in the November election.
Mr Booker, the only African-American to make Mrs Clinton's shortlist, argued that the presence of a black running mate would motivate black voters, helping Mrs Clinton re-create the coalition that backed former president Barack Obama in 2008 and 2012.
But Mrs Clinton had won the Democratic nomination with substantial black support, and some of her advisers argued that many black voters would already be energised by Mr Trump's divisive candidacy and appeals to white conservatives, according to several people involved in the selection.
She chose Senator Tim Kaine of Virginia, a white moderate widely seen as a safe, traditional pick.
No two presidential cycles are completely analogous, but as former vice-president Joe Biden begins his search for a running mate, Mrs Clinton's loss and the weaker-than-expected black turnout in 2016 are on the minds of top Democrats.
Mr Biden has already committed to selecting a woman, and he and his allies have repeatedly mentioned two black women as possibilities - Senator Kamala Harris of California and Ms Stacey Abrams, the party's 2018 nominee for governor of Georgia - as well as several white women, particularly Senator Amy Klobuchar of Minnesota and Governor Gretchen Whitmer of Michigan.
Pressure has been growing on Mr Biden to choose a black woman to inspire black turnout this fall and not take it for granted.
The Reverend Al Sharpton, for instance, who speaks to Mr Biden regularly, is to announce his support for Ms Abrams as vice-president as soon as this week, according to those familiar with his plans.
Yet Mr Biden is facing other factors and pressures as well. He has said he wants someone who is prepared to step into the vice-presidency immediately, a nod to the value he puts on government and leadership experience.
He would be the oldest president ever, at 78 on Inauguration Day, and is looking for a partner and, possibly, a potential successor.
With the country deep into the coronavirus pandemic, voters will also assess whether his running mate appears capable of handling the worst national crisis since World War II.
Ms Harris, who has statewide and national experience, is seen in the Biden camp as a more likely pick than Ms Abrams, who was a state legislative leader for a decade before losing her bid for governor.
Still, some Democrats believe that choosing a hands-on governor or veteran senator is a better fit for the crisis than Ms Harris, who was attorney-general of California and has been in the Senate for three years.
Mr Biden's selection has also become a vehicle for a broader debate among Democrats about the best strategy to win back the White House.
While candidates like Ms Harris or Ms Abrams could energise core Democratic constituencies such as black voters or younger voters, as well as women, Ms Whitmer and Ms Klobuchar could be a geographic plus, considering they hail from the Upper Midwest region important to the Electoral College.
Among some black leaders and activists close to Mr Biden, including Representative Jim Clyburn of South Carolina and former Democratic Party chair Donna Brazile, a commitment to selecting a woman is not enough. They have publicly and privately pushed Mr Biden to select a black woman, arguing black voter enthusiasm may hinge on it.
There is no precedent for the selection of a black running mate. There is also little evidence that vice-presidential selections sway general elections in any meaningful way, including Mrs Clinton's selection of Mr Kaine in 2016.
Still, citing the dip in black turnout four years ago, and the importance of black urban centres such as Milwaukee, Philadelphia, Detroit and Cleveland in the Electoral College, proponents like Rev Sharpton argue that a black woman could help Mr Biden.
Mr Biden said he had already committed to nominating a black woman for the Supreme Court. "I'll commit to that... because it is very important that my administration look like the public, look like the nation," he said.
"There will be a woman of colour on the Supreme Court. That doesn't mean there won't be a vice-president, as well."