While Mr Donald Trump zeroes in on his vice-presidential pick for the Republican campaign, Mrs Hillary Clinton's choice for her Democratic running mate is seen as more open and fluid at the moment.
She is expected to name her choice sometime after the Republican National Convention ends and before her own convention begins in Philadelphia on July 25.
Here are five names who are fancied to be on Mrs Clinton's ticket.
As the chairman of the House Democratic Caucus, Mr Becerra is the highest-ranking Latino in the House.
He had turned down President Barack Obama's offer to be the US trade representative in 2008, saying he would have more influence in Congress, which he was elected to in 1992.
The 58-year-old Sacramento native has stumped for Mrs Clinton in both English and Spanish and is tipped to be a powerful voice for her on immigration matters.
A Latino politician also brings an appealing contrast to Mr Trump's controversial remarks against Mexican immigrants.
The two-term senator from Ohio could help with attracting blue-collar Democrats who might be persuaded by Mr Trump's populist appeal.
When it comes to labour issues, Mr Brown is viewed as a solid surrogate for Mrs Clinton. He is known for his opposition to free trade deals and helped rally Republicans and Democrats against the North American Free Trade Agreement (Nafta) in 1993.
However, his sharp temper may not be beneficial to Mrs Clinton's hopes of reaching moderate Republicans who do not back Mr Trump.
James G. Stavridis
The New York Times reported that Mrs Clinton's campaign is vetting Mr Stavridis, a retired four-star Navy admiral who served as the 16th supreme allied commander at Nato.
Fulfilling Mrs Clinton's desire for someone with military experience, he oversaw operations in the Middle East - Afghanistan, Libya and Syria - as well as in the Balkans and piracy off the coast of Africa.
In 2012, Mr Stavridis was investigated for the alleged improper use of a military aircraft to fly with his wife to a party in France with winemakers. He was subsequently cleared of misconduct after a Pentagon investigation into his travel and expenses, including trips he took with his wife, daughter and mother.
Seen as the Democratic Party's rising star, Mr Castro became the youngest mayor of a major US city when he was elected to helm San Antonio in 2009 at the age of 35.
A lawyer by training, he earned national attention with his keynote speech at the 2012 Democratic national convention, and would be a hit with Hispanics feeling alienated by Mr Trump's immigration rhetoric.
While his youth and charisma could prove to be an asset to 68-year-old Mrs Clinton, his lack of experience in Washington is a concern.
Virginia's junior senator served as Democratic National Committee chairman for two years, and was on President Obama's shortlist for running mate in 2008.
Mr Kaine endorsed Mrs Clinton early in her campaign, and it helps that he comes from a swing state and has good relationships on both sides of the aisle.
Seen as a more traditional and safe choice for VP, the 58-year-old is a fluent Spanish speaker with blue-collar roots and focused his law practice on housing discrimination.
Sources: New York Times, CNN, USA Today, Huffington Post