FILE - In this June 17, 2016, photo, Housing and Urban Development Secretary Julian Castro addresses the Texas Democratic convention in San Antonio. Hillary Clinton’s search for a running mate is moving into a more intense phase, according to several Democrats, as aides contact a pared down pool of candidates to ask for reams of personal information and set up interviews with the vetting team. Those on the shortlist include Sen. Elizabeth Warren, D-Mass., Sen. Tim Kaine, D-Va., and Castro.(AP Photo/Eric Gay)
FILE - In this June 17, 2016, photo, Housing and Urban Development Secretary Julian Castro addresses the Texas Democratic convention in San Antonio. Hillary Clinton’s search for a running mate is moving into a more intense phase, according to several Democrats, as aides contact a pared down pool of candidates to ask for reams of personal information and set up interviews with the vetting team. Those on the shortlist include Sen. Elizabeth Warren, D-Mass., Sen. Tim Kaine, D-Va., and Castro.(AP Photo/Eric Gay) Credit: Eric Gay

Washington — Hillary Clinton’s search for a running mate is moving into a more intense phase, according to several Democrats, as aides contact a pared-down pool of candidates to ask for reams of personal information and set up interviews with the presumptive Democratic nominee’s vetting team.

Those on the shortlist include Massachusetts Sen. Elizabeth Warren, a favorite of progressives who has emerged as a blistering critic of presumptive Republican nominee Donald Trump; Virginia Sen. Tim Kaine, a well-liked lawmaker from an important general election battleground state; and Housing and Urban Development Secretary Julian Castro, of Texas, a rising star in the Democratic Party.

Vermont Sen. Bernie Sanders is not on the list, according to one Democrat.

A small group of Clinton campaign confidants has been sifting through publicly available information about more than two dozen possible contenders for more than a month. But with Democratic primary voting wrapping up last week, the list has been culled significantly and the campaign has begun contacting those under consideration.

If Clinton were to tap Warren as her No. 2, she would be choosing one of the Senate’s most outspoken liberals and a proponent of tough Wall Street regulation. Warren has long been viewed as a running mate who could help Clinton appeal to Sanders’ loyal supporters. She is also relishing taking on Trump, blasting the businessman in speeches and on Twitter as a “thin-skinned, racist bully” — embracing a running mate’s traditionally aggressive role.

While Warren and Clinton do not have a close relationship, they recently met for about an hour in Washington.

Kaine, a former Virginia governor who previously headed the Democratic National Committee, is well-liked within the party and is more moderate than Warren. While he may not excite liberals, he’s seen as a running mate who could appeal to independents and swing voters in his home state and elsewhere.

President Obama thoroughly vetted Kaine as he searched for a running mate in 2008.

Castro, a telegenic 41-year-old, would bring youthful enthusiasm to Clinton’s campaign and would be the first Hispanic on a major party ticket.

Obama plucked him from his post as San Antonio mayor in 2014 to serve in the Cabinet, a move seen by some Democrats as a way to bolster Castro’s national profile for a potential vice presidential run.