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Every four years, summer brings with it a popular parlor-game among even the most casual political observers. Who will the presidential nominee(s) pick as their running mate?

Donald Trump has said he's seeking a governing partner who understands the ins and outs of policy-making. Here's a look at some of the top contenders for the job -- and who's in the top tier, in the hunt and on the bubble.

TOP TIER: Gov. Mike Pence

Indiana Gov. Mike Pence delivers his State of the State address to a joint session of the legislature at the Statehouse in Indianapolis. Pence declined to say whether he would sign a shelved bill to expand protections for lesbian, gay and bisexual people. Pence spoke to reporters after filing for re-election for a second term Wednesday. (AP Photo/Darron Cummings) Darron Cummings / AP, file

Current job: Governor of Indiana.

Reputation, in one sentence: A former congressman, lauded by social conservatives, who’s had a sometime bumpy tenure at the helm in Indiana

Strengths: Picking Pence would bolster Trump’s credentials with conservatives, especially as a band of GOP delegates tries to thwart Trump at the convention. Pence also would give the GOP ticket congressional and gubernatorial experience.

Weaknesses: Pence is currently running for re-election, and Indiana law bars him from running for both VP and governor – and he has until July 15 to remove his name from the Indiana ballot. So Trump picking him could potentially cost Republicans a gubernatorial contest (although Pence is in no way guaranteed to win if he stays on the ticket, either.) Then there’s the backlash from Pence signing into law religious-freedom legislation that critics said allowed businesses to discriminate against gays and lesbians for religious reasons.

TOP TIER: Former House Speaker Newt Gingrich

This March 8, 2014, file photo shows former House Speaker Newt Gingrich addressing the Conservative Political Action Conference annual meeting in National Harbor, Md. Cliff Owen / AP

Current job: Fox News contributor; adviser at Dentons law firm; author & public speaker.

Reputation, in one sentence: Led the 1994 “Republican Revolution,” passing sweeping legislation under the “Contract with America.”

Strengths: He’d certainly offer Trump legislative and congressional experience. And Gingrich has endured the scrutiny – and slings and arrows – of being a presidential candidate in 2012 and House speaker in the 1990s.

Weaknesses: A Trump-Gingrich ticket would feature a combined six marriages between the two men. And if Trump wants to score points off of Monica Lewinsky and the Bill Clinton sex scandals, Gingrich could complicate that effort – given Gingrich’s own extramarital affair during Clinton’s impeachment.

TOP TIER: Gov. Chris Christie

New Jersey Gov. Chris Christie speaks in Washington in 2015. Alex Wong / Getty Images file

Current job: Governor of New Jersey.

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Reputation, in one sentence: An unapologetic Republican governor of a blue state who “tells it like it is”

Strengths: As Trump’s first major endorser, Christie makes sense on several levels – he’s combative and controversial (just like Trump is), he speaks his mind (ditto), and he’s a two-term governor to boot. And Christie has already been named chairman of Trump’s transition team.

Weaknesses: Christie probably doesn’t help Trump in New Jersey; in fact, a June 6 Monmouth University poll shows him with a dismal 27 percent job approval rating. And while it has disappeared from the headlines, that Bridgegate scandal hasn’t 100% concluded – and that could be potentially problematic in the fall.

IN THE HUNT: Sen. Jeff Sessions

Sen. Jeff Sessions, R-Ala., pauses as he takes his seat on Capitol Hill in Washington, Monday, Oct. 19, 2015. Carolyn Kaster / AP

Current job: United States Senator from Alabama. Serves on the Judiciary Committee and chairs its immigration subcommittee.

Reputation, in one sentence: The Senate’s most vehement opponent of comprehensive immigration reform.

Strengths: If Trump wants to double down on the issue of immigration, Sessions makes sense – given that he’s one of the most ardent opponents of both illegal and legal immigration in Congress. Sessions also would add legislative/congressional experience to the ticket. And Sessions was an earlier endorser of Trump.

Weaknesses: Picking Sessions wouldn’t add a lot of ideological diversity to the ticket, and it certainly wouldn’t win over many Latino voters. In the 1980s, Sessions was blocked from becoming a federal judge after a former deputy accused him of making racially insensitive comments. “The former deputy, Thomas Figures, who was an assistant United States Attorney for seven years, said in a written statement that Mr. Sessions once admonished him to be careful about what he said 'to white folks.' Mr. Figures is black,” the New York Times wrote back then. Sessions also was accused of mishandling a voter-fraud case against civil-rights activists.

IN THE HUNT: Gov. Mary Fallin

Oklahoma Republican Governor Mary Fallin. MIKE THEILER / Reuters, file

Current job: Governor of Oklahoma.

Reputation, in one sentence: First female governor of Oklahoma and a staunch conservative.

Strengths: If Trump is looking to add a woman to the ticket to counter Clinton’s historical candidacy, Fallin could very well be the pick. She also served two terms in Congress before becoming Oklahoma governor. And she’s more than open to being considered for the VP job. "My first and foremost goal right now is to finish our legislative session, but if I were to receive a call that said: 'I need you to help make America great again,' I'd be happy to take that call,” she said.

Weaknesses: Hailing from red Oklahoma, Fallin doesn’t help expand the battleground map. And she’s never been considered one of the rising stars of her party – the same way that Gov. Nikki Haley and Sen. Marco Rubio were from that GOP Class of 2010.

IN THE HUNT: Sen. John Thune

Sen. John Thune, R-South Dakota, is highly unlikely to "friend" founder Mark Zuckerberg on Facebook. AP -- file

Current job: United States Senator from South Dakota. Currently serves as Senate Republican Conference chairman, the third-ranking lawmaker in GOP Senate leadership.

Reputation, in one sentence: A telegenic party leader and strong fundraiser long considered a rising GOP star.

Strengths: As the No. 3 Republican in Senate leadership, Thune as Trump’s VP would further signal that the Republican establishment is coming around to Trump. He also would add congressional and legislative experience to the ticket. And Thune comes straight out of presidential central casting – tall, handsome, telegenic.

Weaknesses: But selecting the establishment Thune would undercut one of Trump’s selling points – that he’s taking on Washington from the outside; Thune is about as inside as you can get. As the senator from red South Dakota, Thune also doesn’t expand the map for Republicans.

Florida Gov. Rick Scott smiles as he speaks in Fort Lauderdale, on Sept. 10, 2013. Wilfredo Lee / AP

ON THE BUBBLE: Gov. Rick Scott

Current job: Governor of Florida.

Reputation, in one sentence: A political survivor who’s struggled with intra-party strife and low approval ratings.

Strengths: Before there was Donald Trump in 2016, there was Rick Scott in 2010 and 2014 – a man who used his wealth to win office in one of the most competitive states in the country. And if Trump wants help in all-important Florida, Scott could help, especially with the state’s unemployment rate declining from above 10.0% when he took office to 4.9% now.

Weaknesses: But how much could he help? Both of Scott’s wins came in midterm years when Democratic turnout was low. And despite his gubernatorial victories, Scott has never been a beloved political figure – see that video of him getting heckled at a Starbucks. Oh, and there’s his work at Columbia/HCA hospitals, which was fined $1.7 billion by the U.S. government for health-care fraud committed while Scott was CEO there.

Senator Scott Brown (R-MA) pauses as he addresses supporters during a campaign rally in Wakefield, Massachusetts November 1, 2012. REUTERS/Jessica Rinaldi (UNITED STATES - Tags: POLITICS ELECTIONS USA PRESIDENTIAL ELECTION HEADSHOT) - RTR39VQ7 ?(C) Jessica Rinaldi / Reuters / Reuters

ON THE BUBBLE: Scott Brown

Current job: Political contributor for FOX News, attorney, New Hampshire political activist

Reputation, in one sentence: Stunned the political world with his 2010 upset victory but hasn’t been able to catch lightning in a bottle since.

Strengths: Brown was a relatively earlier endorser of Trump, and helps him in the battleground state of New Hampshire (although this again raises the question: Which is Brown’s real home state – New Hampshire or Massachusetts?) And Brown’s views on immigration are consistent with Trump’s.

Weaknesses: Many GOP conservatives might find this disqualifying about Brown: He supports abortion rights. “Scott Brown is pro-choice and will protect a woman’s right to choose,” his 2014 Senate campaign spokeswoman said back then. And so adding Brown to the ticket could be problematic for Trump, whose credentials on social issues are already somewhat shaky. Brown also voted to ratify the New START treaty with Russia, which was one of Clinton’s top achievements as secretary of state, complicating Trump’s message hitting Clinton’s foreign-policy record. And Brown lost his last two statewide races (in Massachusetts in 2012 and New Hampshire in 2014).