Key Democratic candidates:

US Democratic presidential candidate Hillary Clinton speaks at a campaign event in Carroll, Iowa January 30, 2016.[Photo/Agencies]

A former first lady, Hillary Clinton served as Obama's top diplomat from 2009 to 2013 after her loss in the 2008 Democratic primary to Obama.

Before the 2008 election, Clinton also served as New York senator and her ties to the Wall Street sometimes become a bit of fodder for her critics.

During this election cycle, in the face of surging support for Bernie Sanders in the Democratic Party, Clinton seeks to portray herself as a progressive that can make progress and work with a Republican-controlled Congress.

Though showing her support for Obama, who still enjoys large popularity among Democrats, Clinton has taken positions at odds with Obama on trade, the Keystone pipeline, etc.