Both Hillary Clinton and Donald Trump are turning their attention to the general election, and to one of the most important decisions they will make —choosing a vice president.

Picking a vice president is the first "presidential level" decision any candidate makes. Although vice presidential candidates have rarely, perhaps never, determined the outcome of an election, the choice tells voters a lot about the candidate.

The two most important criteria are always the same:

1. Pick someone who's would ready to be president, if necessary, and
2. DO NO HARM

Here's a look at the potential VP short lists for Clinton and Trump. For the purposes of this exercise, we will restrict the names to those who have indicated they would be open to the possibility or at least have not ruled out joining the ticket.

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Trump

The Republican has an unusual VP search, because so many prominent Republicans have ruled out joining his ticket. But he still has plenty of eager running mates to choose from. Trump told the AP this week that he's narrowed his search to five or six people. He's said he'd like someone with political and legislative experience to help him deal with congress, and he's also said he'd consider some of his former rivals. Here are three categories the potential picks fall in (bolded are possible vice presidential picks):

1. Former opponents

Both Rick Perry and Bobby Jindal have endorsed Trump. Both are former governors. But Trump will probably win Texas and Louisiana without them.

New Jersey Gov. Chris Christie was one of Trump's earliest establishment endorsers, and Trump has asked him to lead his transition team. Christie's in-your-face, tough-talking style is a lot like Trump's. If being an attack dog is a top requirement for a VP candidate then Christie's evisceration of Marco Rubio is a qualification/ recommendation. Then again, Trump usually takes care of those duties himself.

John Kasich, Ted Cruz and Rubio all fit Trump's criteria, though Rubio has ruled it out, and it's hard to see Kasich or Cruz on the ticket after their previous brutal fights with Trump.

2. Members of Congress — current and former

Former House Speaker Newt Gingrich knows something about running against the establishment. He's made it clear he'd be happy to be on the ticket.

Bob Corker, Senate Foreign Relations Committee chairman and former businessman, has lavished praise on Trump for his recent foreign-policy speech and has said he wouldn't rule out the VP slot.

3. The "woman's" card

Trump said this week he might consider Jan Brewer, the former governor of Arizona, who shares his position on immigration; Or Joni Ernst, a freshman senator elected with Tea party support. Ernst has been critical of Trump's comments about women, but she hasn't ruled out taking the VP spot. Trump's negatives with women are sky high. A woman on the ticket might help. Plus, Ernst is from the swing state of Iowa.

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Clinton

The Democrat, like Trump, is already vetting VP candidates, and her possible picks fall into three categories:

1. Swing-state senators

Sherrod Brown from Ohio says he;'s " not interested" but hasn't made a Shermanesque statement ruling out the VP spot. He could be helpful if Clinton needs support in the important battleground state of Ohio. Brown is a great communicator, who does well with the kind of white, blue-collar voters who have voted for Bernie Sanders and Donald Trump. (Plus, Brown has a wife who won a Pulitzer Prize.) One potential downside — if Clinton wins, a Republican governor would fill Brown's vacant Ohio seat.

Then there's Tim Kaine who has been an effective, if not very charismatic, surrogate for Clinton. He's from Virginia, an important battleground state for Democrats, and Kaine speaks fluent Spanish.

2. Hispanic Cabinet Secretaries

Julian Castro is the secretary of the department of Housing and Urban Development, or HUD. He's also the former mayor of San Antonio, Texas, and he's a telegenic, young Mexican-American. Tom Perez, the Labor secretary, is Dominican-American. Both could help Clinton with Hispanic voters, if she decides Trump isn't helping her enough there already.

3. Play another woman card, or base card

Elizabeth Warren is the heroine of the progressive left. She could help Clinton bring in Sanders voters, if Clinton decides that she (and Trump) can't do that alone. Warren has also shown she has the stomach for a bare-knuckle brawl with Trump. She's been engaged in a Twitter war with the likely Republican nominee. He calls her "Goofy" Elizabeth Warren, and she calls him a narcissist and a racist.

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