USA TODAY VP Power Rankings: Kaine tops the list for Clinton's running mate

Once she locks down the Democratic presidential nomination, Hillary Clinton faces the daunting task of mobilizing progressive activists and outsiders who backed Bernie Sanders as well as the black and Hispanic voters she relied on to beat him.

But our panel of experts thinks her most likely vice presidential pick is Tim Kaine, the moderate Virginia senator and former governor who is the consummate party insider, having once served as Democratic National Committee chairman.

Our experts — the same folks who provided our weekly GOP Power Rankings in the fall and winter — offered a variety of candidates who could help Clinton shore up support with minority voters and liberals: New Jersey Sen. Cory Booker, who is young, African-American and the king of social media; Rep. Xavier Becerra, the only Latino holding a Democratic leadership post in Congress; and Secretary of Labor Tom Perez, a hero of organized labor.

Diversity is not a new concern for the Democrats. It is worth recalling that in early 1993, President Bill Clinton arrived in Washington with a mandate for his personnel office: New federal appointees had to reflect ethnic, gender and geographic diversity, which became known as "EGG."

Nevertheless, the runaway favorite among our group of experts is Kaine, a white male who lives a few hours drive from D.C. "Tim Kaine is far and away the best choice — former mayor, governor, Spanish speaking, highly regarded from a swing state." said Dallas Morning News columnist Carl Leubsdorf. "I expect Hillary Clinton to pick someone clearly qualified to be president, to increase the contrast with Trump."

Prep for the polls: See who is running for president and compare where they stand on key issues in our Voter Guide

Former Democratic congressman Dan Maffei said Kaine "helps a little with Obama insiders but could really help win Virginia."

Sen. Sherrod Brown, an Ohio senator, also scored well among our panel, both because the Buckeye State is critical for the general election and because he is more trusted among the party's liberals than Clinton is.

Clinton "is likely to choose a running mate with whom she can work — so it might be someone she already knows or has worked with already," said Carroll University professor Lilly Goren. Picking Brown or Massachusetts Sen. Elizabeth Warren would "signal to many of the Sanders supporters that she is bringing their positions and advocates into the campaign," Goren said.

The panel offered a wide range of potential candidates, ranging from Minnesota Sen. Amy Klobuchar ("She can be very biting, caustic and yet funny ... a bad combination for the Donald," said Democratic pollster Peter Fenn) to Housing and Urban Development Secretary Julian Castro ("Clinton needs to freshen up her campaign/image and the best way to do that is to introduce a new name to the national stage," said Craig Robinson, editor of The Iowa Republican).

One pick would bring about a different kind of diversity: Digital guru Alan Rosenblatt said Clinton should select Minnesota Sen. Al Franken, because "he balances the ticket by adding an unforced sense of humor."

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Participants in USA TODAY's VP Power Rankings:
Paul Brathwaite , principal, Podesta Group
Dianne Bystrom, director, Center for Women and Politics, Iowa State University
Frank Donatelli, former RNC deputy chairman and Reagan adviser
Peter Fenn, Democratic political strategist, Fenn Communications
Andra Gillespie, polling analyst and political science professor, Emory University 
Nathan L. Gonzales, editor, The Rothenberg & Gonzales Political Report
Lilly J. Goren, political science and global studies professor, Carroll University
Doug Gross, Iowa attorney and previous Republican gubernatorial nominee
O. Kay Henderson, news director, Radio Iowa
Ken Khachigian, senior partner, Brownstein Hyatt Farber Schreck
Carl Leubsdorf, Washington columnist, The Dallas Morning News
Deb Lucia, Topeka 912 – the Capital City Tea Party
Matt Mackowiak, Republican consultant and president, Potomac Strategy Group, LLC
Dan Maffei, former Democratic congressman, New York
Jon Ralston, host, "Ralston Live" on PBS affiliates in Nevada
Craig Robinson, founder and editor, TheIowaRepublican.com
Alan Rosenblatt, Ph.D., Sr. VP of digital strategy, turner4D
Adam Sharp, head of news, government and elections, Twitter
Alex Smith, national chairman, College Republicans
Kathy Sullivan, DNC committeewoman and former Democratic Party chair, New Hampshire