Now that Donald Trump is the presumptive Republican presidential nominee and Democrat Hillary Clinton is the almost-presumptive nominee, attention is shifting to their choices for running mates.

Trial balloons, leaks, faux demurrals, rampant speculation and blatant kissing up will play out in anticipation of big unveilings before July’s conventions. Typically, nominees want someone with experience they don’t have or the ability to deliver a key state.

REPUBLICANS

Jan Brewer,  former Arizona governor

Assets: She became a conservative icon during her tenure as governor and said this month that she’d be “willing.” Trump, who needs to do something to appeal to the women voters who have spurned him so far, has called her “fantastic.”

Challenges: She doesn’t really have a national following and she would be compared to Sarah Palin, another Western governor.

Ben Carson, former presidential candidate

Assets: He pledged fealty to Trump soon after his own campaign ended and is heading the search for a running mate. And he would add diversity to the ticket.

Challenges: He’s never been elected to anything, and Trump has been pretty clear about wanting a running mate who can help him navigate the minefields on Capitol Hill.

Chris Christie,  New Jersey governor

Assets: He became the first sitting governor to endorse Trump in February, and the presumptive nominee clearly trusts him: Christie is in charge of his White House transition team.

Challenges: Voters did not fall in love with him during his own presidential campaign and he won’t put New Jersey in play — the state is almost certain to go to the Democrats.

Bob Corker,  Tennessee senator

Assets: He’s chairman of the Foreign Relations Committee and that expertise would plug a notable gap in Trump’s résumé. He’s the sort of D.C. insider Trump says he wants.

Challenges: He criticized Trump’s call for banning all Muslims from entering the U.S. They met for the first time last week, so they would need to book some quality bonding time.

Joni Ernst,   Iowa senator

Assets: She made a name for herself with her feisty 2014 Senate campaign and Iowa Gov. Terry Branstad is pushing hard for Trump to consider her. She’s known for being a team player and is a retired National Guard commander.

Challenges: Would a first-term senator match Trump’s inclination to choose a Washington insider?

Newt Gingrich,  former House speaker

Assets: He’s a cerebral inside player, has been an unabashed Trump supporter since before it was cool and has the Washington experience that Trump says he wants.

Challenges: Years out of the political limelight might make him seem like a throwback choice and, like Trump, he has a personal history that’s, well, complicated.

John Kasich,  Ohio governor

Assets: No Republican has ever won the presidency without carrying Ohio. Ever. That really matters.

Challenges: He’d have to be talked into it and explain why he changed his mind. Before Kasich suspended his presidential campaign, spokesman Chris Schrimpf said that Kasich would “never” consider it. “No chance,” he said.

Sarah Palin,  former Alaska governor

Assets: She’s (still) entertaining, fearless and retains her skill for getting herself on cable TV news shows. Her experience as Sen. John McCain’s 2008 running mate might help (or it might not). And she loves Trump and has a disdain for Washington that fits with this year’s voter tendencies.

Challenges: Oh, you know.

Rick Perry,  former Texas governor

Assets: Two-time presidential candidate has made it clear that he’s interested. “I will be open to any way I can help,” he said.

Challenges: Choosing Perry — who last year called Trump a “cancer on conservatism” — would be a test of Trump’s capacity for forgiveness. And his memory. Perry would have to debate his Democratic counterpart, and he has a wobbly debate history.

Scott Walker,  Wisconsin governor

Assets: Wisconsin is a swing state and Walker remains very popular there. Trump has said that he likes the governor, who is still admired by conservative voters for taking on public employee unions. He’d bring youth (he’s 48) to the dance.

Challenges: When he exited the presidential race, Walker slammed Trump. Then he endorsed Texas Sen. Ted Cruz.

DEMOCRATS

Cory Booker,  New Jersey senator

Assets: He’s black and has a record of accomplishment as Newark’s mayor. He speaks Spanish and is an enthusiastic campaigner who could woo some Bernie Sanders backers.

Challenges: He was one of the Senate’s biggest recipients of campaign money from Wall Street in 2014. New Jersey Gov. Chris Christie would appoint a Republican successor.

Sherrod Brown,  Ohio senator

Assets: Like Clinton, he opposed President Obama’s trade deals. The attack-dog part of the gig might appeal to him. And denying Donald Trump a win in Ohio could be the whole ballgame.

Challenges: His Senate seat would go to a Republican if he joins the ticket. He has said out loud that he’s not interested, but that might or might not matter (see demurrals, above).

Julian Castro,  HUD secretary

Assets: He’s young (41), a high-profile Latino and a compelling speaker. A former San Antonio mayor, he’d help Democrats in a key state, and he could motivate younger voters.

Challenges: He’s young and might need more seasoning before he’s ready for a national campaign. He has had some growing pains in the Cabinet, including some rocky Capitol Hill hearings.

Al Franken,  Minnesota senator

Assets: He’s already famous, quick-witted enough to throw Trump off his game and a formidable fundraiser. His affable persona could be an effective counterpoint to Clinton’s serious mien. There’s already an alfrankenvpwatch.com website.

Challenges: Minnesota isn’t likely to be competitive and he seems genuinely disinterested in the job.

Tim Kaine,  Virginia senator

Assets: A former governor and Christian missionary who’s fluent in Spanish, he’s widely admired for his moderate views. He’s a low-profile, non-controversial political pro.

Challenges: Those views might be too moderate for many voters, and he’s been the focus of so much speculation that he could end up seeming like a ho-hum, safe choice.

Amy Klobuchar,  Minnesota senator

Assets: The consensus on Capitol Hill is that she’s an up-and-coming star (the Washington Post said so). An all-female ticket would make history, and her Senate seat would go to a Democrat appointed by Gov. Mark Dayton.

Challenges: Clinton is likely to win Minnesota without a boost from her. A two-woman ticket might be a gamble.

Deval Patrick,  former Massachusetts governor

Assets: He’s black, would add diversity to the ticket and buzz suggests that he’s under active consideration.

Challenges: Back in 2014 he called for a strong primary challenge to Clinton, and he now works for Bain Capital, a much-criticized private equity firm founded by former democratic presidential candidate Mitt Romney.

Tom Perez,  labor secretary

Assets: The son of immigrants, he’s being called a “sleeper” pick who hit it off with Clinton after endorsing her in Iowa. He could be attractive to Latino voters and would help signal a continuation of some Obama policies.

Challenges: He isn’t a household name and has no broad policy expertise. Clinton has ceded economic policy to her spouse.

Bernie Sanders, Vermont senator and  presidential candidate

Assets: He won plenty of primaries and caucuses and has an enthusiastic following that includes crucial young and independent voters who might otherwise stay home.

Challenges: He’s 74, which could raise questions about his ability to step into the top job. The animus between him and Clinton might be hard to overcome, though.

Elizabeth Warren,  Massachusetts senator

Assets: She’s a popular progressive who could help unify the party. Her efforts to rein in Wall Street would appeal to the voters who opted for Sanders in the primaries. She’s been taking on Trump aggressively lately. A tryout?

Challenges: She probably wields more power as a senator, and she didn’t endorse Clinton.