“Senator Catherine Cortez Masto is a trailblazer who has the legislative and executive experience needed to serve our country during these times of crisis,” argued Sen. Jacky Rosen (D-Nev.). “I cannot think of anyone better to become the first female vice president of the United States of America.”

Biden served alongside Amy Klobuchar of Minnesota; as vice president, he worked with Sens. Elizabeth Warren of Massachusetts and Tammy Baldwin of Wisconsin as well as Tammy Duckworth of Illinois while she was in the House. He campaigned for Cortez Masto of Nevada in 2016 and this year ran against Sen. Kamala Harris of California, Klobuchar and Warren for the Democratic nomination.

Michigan Gov. Gretchen Whitmer, Rep. Val Demings (D-Fla.) and former Georgia House Minority Leader Stacey Abrams are also in the mix. And though Abrams is making an overt push, the sheer number of Democratic senators in the running makes the senators the favorites.

The crowd of female senators for Biden to choose from reflects the broader trend of more and more women seeking higher office — so much so that the women-only veepstakes is playing out under the radar. This year brought an unprecedented selection of female candidates running for president, and the 2018 midterm elections led to a historic number of women elected to Congress. Just four years ago, Hillary Clinton became the first female presidential nominee of a major party.

Meanwhile, the jockeying to be the former vice president’s vice president is just beginning. Klobuchar has appeared on Biden’s podcast, Harris appeared with Biden at a fundraiser and Warren has publicly said she’d take the job. The two Midwestern Tammys and Cortez Masto have been less visible, but are no less viable contenders for the role.

“With Biden, he’s only going to consider women, which I think is progress,” said Sen. Mazie Hirono (D-Hawaii.). And “the names that I’ve seen: Most of them are female senators. I think that advances the odds.”

Asked how Biden might choose from the half-dozen Democratic senators, Sen. Patty Murray (D-Wash.), the second-longest serving female senator, replied: “I’m just glad he’s doing it.”

But while Biden’s vow is viewed by many Democratic women as notable, it doesn’t compare to the “oh my goodness” moment when Walter Mondale picked Geraldine Ferraro in 1984, said former Sen. Heidi Heitkamp (D-N.D.).

“Hillary being the nominee four years ago and then Elizabeth being incredibly competitive and Amy being competitive and Kamala being competitive, even Tulsi Gabbard. People see women on the stage and the more that happens, the more normalized that becomes,” Heitkamp said.

The Senate is a longstanding recruiting ground for Democratic vice presidential candidates, and for Biden it’s likely no different. Simply by the numbers, a female Democratic senator is the odds-on favorite for being selected. Ferraro was the most recent vice presidential candidate not to come from the upper chamber.

And there’s still plenty of groundbreaking possibilities. Harris would be the first black woman selected as a vice presidential pick, while Cortez Masto is the first Latina senator. Duckworth would be the first Asian American woman to share the ticket, and is also a combat veteran and double amputee. Baldwin was the first openly gay senator when elected in 2012.

Warren would be the most liberal vice presidential pick in a generation, while Klobuchar hails from a state and region on which Trump’s electoral fortunes might depend.

Nevada Sen. Catherine Cortez Masto is one of the Senate women that Joe Biden might be considering. | Alex Brandon/AP Photo

“They’re all different and unique in their own way,” Murray said.

While the competition for vice president is not always subtle, the coronavirus pandemic is changing that dynamic by limiting a candidate’s events and fundraisers to virtual gatherings.

And with the Senate away from Washington until at least May 4, any campaigning among Senate colleagues for the No. 2 spot is going on even less explicitly.

“We don’t see a lot of it because we’re not together,” said Sen. Chris Murphy (D-Conn.). “Do I see any jockeying happening? And the answer is no. I don’t.”

Senators are focused instead on dealing with the public health and economic crises in their states. When asked recently about her interest in becoming vice president, Harris responded: “I am not thinking about that.” Cortez Masto, who chairs the Democratic Senatorial Campaign Committee, offered a similar answer.

But that doesn’t mean they’re staying out of the headlines. And the former 2020 presidential candidates are seizing on their national name recognition to roll out proposals to address the coronavirus.

Klobuchar is making an aggressive push to expand vote by mail. Warren is rolling out plans to expand testing, push the government to manufacture medical supplies and increase worker protections. Harris wants to expand early voting and vote by mail.

Baldwin and Duckworth want a temporary protection standard through the Labor Department requiring employers to limit coronavirus exposure for employees.

The Biden campaign is set to announce its vice presidential selection panel by May 1. Democrats don’t expect an actual pick until July.

And personality dynamics will almost certainly play a role.

“When Obama chose Biden, I think there were reservations there,” said Sen. Dick Durbin (D-Ill.), the Senate minority whip. “In short order, Obama realized it was not only the right decision, but the best decision he could have made. They developed a working relationship, and I’ll bet you a nickel that’s what Biden’s looking for, too. He needs somebody he can have good chemistry with.”

The senators in contention have differing styles and strengths. Harris is a probing questioner in Senate Judiciary Committee hearings, while Warren is a watchdog of large financial institutions. Klobuchar and Duckworth are “Midwestern nice” but are nonetheless hard-nosed pols. Baldwin and Cortez Masto are low key but have won important races in battleground states.

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“Tammy Baldwin is a person I respect very much because she doesn’t make a lot of noise,” said Hirono, who doesn't have a favorite. “She just gets things done.”

In 2016, Clinton’s vice presidential selection focused on Democratic senators like Sherrod Brown of Ohio, Tim Kaine of Virginia and Cory Booker New Jersey. As the pick, Kaine helped Clinton easily win Virginia but did little to alter the course of the race.

Some senators say no matter who Biden picks — someone splashy like Warren or reserved like Baldwin — the result may be the same.

“You’ve got to make the right pick but this election is not going to be a referendum on the Democratic vice presidential candidate," Murphy said. "It’s going to be dominated by one enormous personality. And that’s the president of the United States."