Opinion: Finding the perfect running mate is a tough ask, as John McCain will attest. Luckily, this guide sets out the options - and takes a look at how Hillary Clinton's choice of Tim Kaine and Donald Trump's choice of Mike Pence measure up.
Franklyn D Roosevelt's vice president, John 'Cactus Jack' Garner, described the role as "not worth a bucket of warm piss".
Many other vice presidents would likely agree. The job description includes attending state funerals, waiting in case the boss unexpectedly dies, and in the unlikely event the Senate is evenly split, casting the deciding vote.
And yet it's popular among ambitious politicians. It's not a sure route to the presidency (just ask President Gore), but it helps. Fourteen vice presidents have gone on to be president, mostly when the president of the time died. John Tyler only had to wait a month.
While waiting for their moment some are embarrassing and ineffectual (Dan Quayle), while others carry surprising sway themselves (Dick Cheney).
For the very ambitious, there might be no better ticket than that of Donald Trump in this year's election. According to the Kasich camp, when Donald Jnr offered Ohio Governor John Kasich the job he asked him whether he wanted to be the "most powerful vice president in history", in charge of both domestic and foreign policy. When asked what President Trump would be doing, the answer was reportedly "making America great again". The governor wisely declined.
Presuming you can get them to agree, who should you pick as your vice-presidential running mate?
The obvious choice is a useful governing partner but this is too often ignored in favour of a running mate that serves tactical purposes: to win a home state, to appeal to a demographic group or to balance the perceived downsides of the presidential nominee.
Home state advantage
The evidence, however, suggests there is very little home state impact, with running mates lifting the vote in their home state by just 2 percent. If they're from a swing state like Florida or Ohio that might be crucial but otherwise it's a surprisingly small effect.
It has worked though. John F Kennedy picked a popular Texan he personally despised (Lyndon Johnson), in order to help bring in southern votes. He did and they won, but they never got on.
This tactic has also driven some terrible choices. Richard Nixon chose obscure Maryland governor Spiro Agnew to help him win the Mid-Atlantic states, which he did. But Agnew was outrageously corrupt to the extent that Nixon hoped that the threat of a President Agnew might keep Nixon himself safe from resignation.
It didn't. Agnew was forced to resign first in a plea bargain for bribery, and was replaced by Gerald Ford who then replaced Nixon.
The second strategy to consider is choosing a running mate to appeal to a particular pool of voters. John Kerry chose John Edwards to appeal to Southerners. Walter Mondale chose Geraldine Ferraro to appeal to women and the northeast.
Barrack Obama chose Joe Biden as a blue-collar politician from "hard scrabble" Scranton to offset the elite tinge of his own Harvard education, and appeal to the working and middle classes of the swing-state rust belt. It worked.
Balancing is particularly common for age and experience: the old pick the young (Bush/Quayle, McCain/Palin, Clinton/Kaine); the young pick the old (Obama/Biden), the wealthy pick the common man (Romney/Ryan, Trump/Pence). Hillary Clinton has balanced her gender; Barrack Obama balanced his ethnicity.
Hopefully, in future, a male candidate will not think twice before balancing their ticket with a woman and a white candidate will automatically offset their ethnicity in their VP choice. We're not there yet.
The Clinton choice
Hillary Clinton's running mate, Tim Kaine, is very popular in the important swing state Virginia, but that's just one reason for the choice. He makes the ticket less terrifying to sexist men, adds to Clinton's national security strength, speaks Spanish fluently, is Catholic and is personally pro-life, making her ticket more palatable to social conservatives. (He has already opened a (presumably agreed) policy distance with Clinton on abortion that may widen their combined appeal to independents.)
Crucially they are also long-time friends who will campaign and work together easily. He's quite the catch.
The Trump choice
Donald Trump chose Indiana Governor Mike Pence. Indiana is usually safely Republican, so the choice is not about geography. Indeed, if he needs Pence's help to win Indiana, then he's already lost.
Pence is on the ticket to balance some of Trump's perceived negatives. One is his total lack of political experience and Pence has that in spades, but so too did his other finalists Newt Gingrich and Chris Christie. However they were both ultimately too toxic and Christie's cause was not helped by him having helped jail the father of Trump's son-in-law and de facto campaign manager Jared Kushner.
Pence won out because he is a hero to the hard Christian right. He's an Old Testament Christian, angrily anti-abortion and LGBTQ, believing gay marriage will cause societal collapse. Last year he signed into law the Religious Freedom Restoration Act which allows discrimination on religious grounds, enabling business people to refuse service to the LGBTQ community.
His presence as running mate attempts to balance Trump's own very scanty religious CV. It probably wasn't necessary. Clinton, who is a practising Methodist, is so anathema to the hard Christian right that they were likely to hold their noses and vote for the irreligious Trump regardless.
In a PPP poll this week only 36 percent of Trump supporters were sure Clinton didn't have "ties to Lucifer".
When strategy goes bad
Choosing for strategy alone can backfire badly, as the hastily chosen Sarah Palin did for John McCain. While Pence may make Trump more palatable to the extremes of the Christian right he may also make him even less palatable to religious moderates and independents. Pence could ultimately do more harm than good to Trump's chances and not doing harm is the abiding rule of picking a running mate.
Unfortunately for Trump, other safer choices made themselves scarce and Pence was likely the safest option available.
Aim away from your feet
There's just one more thing to consider in choosing your vice president. Don't ever pick a senator from a state with a governor from the other party. In most states that governor gets to pick the replacement and you may gain a vice-president but lose the Senate and so be stymied endlessly, as President Obama has been for much of his presidency.
Good luck and happy choosing.
An update on convention bounces
Last week I talked about the polling effect called a convention bounce. Three types of results are now in.
This returns their relative numbers to about where they were a month ago (but with fewer undecided voters).
Likeability: Clinton's net favourability has improved from a dismal -15 percent a month ago to -6 percent. Trump's net favourability is steady at -22. Ouch.
Convention impact: Since 1984 Gallup has asked voters whether the conventions made them more or less likely to support each party. For the first time ever they got a net negative result. For the Democratic convention the positive/negative split was a close-run 44/42, but the Republican Convention returned 35/52, with more than half the respondents put off by what they saw. As Trump said to ABC News last week, "I've had a beautiful, I've had a flawless campaign. You'll be writing books about this campaign."
*Phil Smith is a journalist who has wasted his adult life revelling in the entertaining minutiae of American politics and culture. He once shared a lunch of rare bison steaks with Jimmy Carter.