Democratic presidential candidate Hillary Clinton, followed by the Rev. Jessie...

Democratic presidential candidate Hillary Clinton, followed by the Rev. Jessie Jackson, arrives to speak at a Rainbow PUSH Women's International Luncheon at the Hyatt McCormick in Chicago, Monday, June 27, 2016. Credit: AP

John Nance “Cactus Jack” Garner of Texas served two terms as vice president starting in 1933. He has been widely quoted as saying that the office “is not worth a bucket of warm spit.” Some say he really cited another substance, but the point remains the same.

Garner presumably was describing what follows inauguration. But during campaigns, running-mate selections are known to count big for symbolism and party unity, if nothing else.

John McCain hoped to give himself a boost in 2008 by picking a younger, female politician for vice president. Some academic studies since showed that Sarah Palin as running mate cost him as much as 2 percent of the vote against then-Sen. Barack Obama.

Discussing the pluses and minuses of each VP prospect means adding up the weaknesses of the nominees-to-be and guessing how a No. 2 pick could compensate for them.

For Donald Trump, some of the conventional thinking goes that he needs someone seasoned in government, which he is not; someone who can raise money, which he has not; someone who can counter his alienation of minorities and women; and someone popular in Ohio and Pennsylvania. 

That’s a lot of compensating for one running mate to handle. And the choices for Trump may be limited. His campaign manager has ruled out “pandering” based on gender or race.

Several of the names mentioned so far instantly suggest drawbacks. The telegenic Sen. John Thune (R-S.D.) has wondered aloud why Trump was in Scotland last week. Gov. Chris Christie might still have Bridgegate problems. Newt Gingrich, at 73, is older than Trump, who at 70 would be the oldest president ever to take the oath.

Sometimes a running mate’s flaws — they all have them — don’t end up hurting the presidential candidate. Before he became vice-president, Joe Biden was known to have lifted a whole speech from one-time British Labour Party leader Neil Kinnock.During the 2008 campaign, he'd also said something weird about then-rival Obama being "clean."

Democrat Hillary Clinton has other problems to solve. Her pick will be examined for progressive views given Vermont Sen. Bernie Sanders’ tough rivalry in the primaries. But she’d also like her running mate to help expand the ticket’s appeal in a general election to independents and Republicans who dislike Trump.

Whether and how it matters that Sen. Tim Kaine (D-Va.) says he is “personally” opposed to abortion undoubtedly comes up for discussion in the Clinton camp. Sen. Elizabeth Warren (D-Mass.), who appeared with Clinton for the first time on Monday, clashed with her years ago over a bankruptcy bill beneficial to credit card companies.

Another consideration for Clinton seems to be the impact of her vice presidential choice on the chances of Democrats winning the Senate in November. If she picked Cory Booker of New Jersey or Sherrod Brown of Ohio, for example, a Republican governor would pick their successors.

Some allies offer their advice openly to the 68-year-old Clinton. “I’d pick somebody under 50 [for vice president]. It’s time for a new generation to take power in Washington, especially in the Democratic Party,” said former Vermont Gov. Howard Dean.

That’s a big bucket of considerations for both parties.