A recently published leaked email from Hillary Clinton Hillary Diane Rodham ClintonDemocratic groups using Bloomberg money to launch M in Spanish language ads in Florida The Hill's Campaign Report: Presidential polls tighten weeks out from Election Day More than 50 Latino faith leaders endorse Biden MORE campaign chairman John Podesta on potential vice presidential picks showed that the campaign considered three retired military leaders, including a retired Navy SEAL.

Podesta wrote in an email dated March 17 suggesting "first cut" veep candidates in "rough food groups."

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Retired Marine Gen. John Allen, retired Navy Adm. Bill McRaven, and retired Navy Adm. Mike Mullen are listed in one group, presumably of military leaders.

Allen delivered a high-profile speech endorsing Clinton at the Democratic National Convention earlier this year, in a move that was criticized by some other retired officers who believe retired military brass should not take such a prominent role in politics, lest the military become politicized.

McRaven, currently the chancellor of the University of Texas and a former SEAL, developed and oversaw Operation Neptune Spear, the special operations raid that led to the death of Osama bin Laden on May 2, 2011.

Mullen, currently a professor at Princeton University, last served as chairman of the Joint Chiefs of Staff, under both Presidents George W. Bush and Obama. Mullen was in the White House situation room with Clinton during the bin Laden raid.

The campaign later vetted Retired Navy Adm. James Stavridis, dean of the Fletcher School at Tufts University, and former commander of NATO Supreme Allied Command-Europe and European Command, for vice president.

Both Trump and Clinton have tried to appeal to veteran and military voters, in a campaign season where national security has been a top issue for voters.

Clinton eventually chose Sen. Tim Kaine Timothy (Tim) Michael KaineDemocrats call for declassifying election threats after briefing by Trump officials Buttigieg stands in as Pence for Harris's debate practice Trump meets with potential Supreme Court pick Amy Coney Barrett at White House MORE (D-Va.), who belonged in one of the "food groups."

Other vice presidential "food groups" included Hispanics, white female politicians, white male politicians, African Americans, CEOs and philanthropists, and Bernie Sanders Bernie SandersOutrage erupts over Breonna Taylor grand jury ruling Dimon: Wealth tax 'almost impossible to do' Grand jury charges no officers in Breonna Taylor death MORE.