June 24 (Bloomberg) -- There was one last thing the lawyer interviewing 1992 vice presidential prospect Al Gore had to ask: In light of Bill Clinton's dalliances, was there any dirt in Gore's personal life that might hinder their election?

Just then a diesel tour bus across the street ``cranked up with a huge roar'' and drowned out Gore's response to him, recalls Harry McPherson, who has advised Democratic presidents and lawmakers since President Lyndon Johnson. Too embarrassed to ask again, McPherson told Clinton's search team that Gore's ``lips seemed to be saying, `There won't be any problem.'''

After the intense public scrutiny of primaries and caucuses that help determine the U.S. presidential nominees, the selection of running mates may seem an oddly secretive, quirky, even undemocratic endeavor.

While nine vice presidents have ascended upon the death or resignation of their bosses, the vetting of would-be ``veeps'' is invisible to all except a few advisers. The under-the-radar campaigns by the hopefuls are ``pitched to a constituency of one,'' says Joel K. Goldstein, a scholar of the vice presidency at St. Louis University Law School.

According to politicians considered for the No. 2 job and people who assessed them for every election since 1976, it's a grueling hiring process that sometimes produces unexpected results. In 2000, Dick Cheney headed George W. Bush's search committee -- and then wound up on the top of the list.

`A Blonde Stranger'

Democrat Bob Graham, who was considered and passed over four times, recalls how investigators called his wife on a 1988 Norwegian vacation to ask about his involvement with ``a blonde stranger.'' The former Florida governor and U.S. senator, now 71, had done a cameo as an adulterous husband in a music video for his musician friend Jimmy Buffett.

The investigators, satisfied there was no infidelity, then asked if Graham had paid taxes on any performance fee. (He says he never received one).

Graham says a magazine profile that portrayed him as eccentric hurt his chances with Gore in 2000. His open-heart surgery worried John Kerry's team in 2004, he adds. Still, Graham doesn't regret the experiences: ``I learned something about myself and how other people perceive me,'' he says.

This year the search has a special intensity. Republican Senator John McCain of Arizona, 71, would be the oldest person to become a U.S. president. (Ronald Reagan was re-elected when he was 73.) Democratic Senator Barack Obama of Illinois, 46, has less than four years of national political experience.

Too Pushy

While ambitious politicians are already signaling interest through influential friends and appearances on television, Michael Dukakis, 74, the 1988 Democratic presidential nominee, cautions against being too pushy. ``I didn't want to be lobbied,'' he says.

``The top of the do's and don'ts list is to not appear to be running for VP,'' agrees Scott Reed, who as campaign manager for 1996 Republican nominee Bob Dole helped choose running mate Jack Kemp. Noisy demands by supporters of New York Senator Hillary Clinton, 60, to add her to Obama's ticket are ``the kiss of death,'' Reed says.

Not since Johnson ran with John F. Kennedy in 1960 has the No. 2 demonstrably helped a nominee win by carrying his home state. Still, the choice is a window into a nominee's decision- making: Candidates often pick someone to compensate for weaknesses or reinforce the campaign message.

Once advisers whittle the possibilities to a short list, teams of lawyers, accountants and private detectives fan out to unearth business deals, unfortunate remarks, forgotten acquaintances -- anything that might come under scrutiny.

Separate Ballots

It wasn't always this way. In the earliest days of U.S. history, the vice president was the presidential hopeful who received the second-most electoral votes. Later, the electoral college voted for president and vice president on separate ballots. Eventually, the second billing on a campaign ticket was awarded at political conventions to placate rival factions.

The job has also evolved from what John Adams, the first vice president, called ``the most insignificant office that ever the invention of man contrived or his imagination conceived.'' President Franklin D. Roosevelt kept Vice President Harry S Truman in the dark about plans to drop an atomic bomb on Japan during World War II. Now, many consider Cheney, with his involvement in national-security policy, the most powerful second-in-command ever.

Electroshock Therapy

Rigorous background checks have become standard practice since 1972, after vice-presidential nominee Thomas Eagleton revealed he'd had electroshock therapy for depression. The disclosure prompted George McGovern to replace him on the Democratic ticket. Today's candidates may be under even tougher scrutiny, fueled by 24-hour news, blogs and YouTube.

Democrat Lee Hamilton, a former U.S. representative from Indiana, recalls being asked in 1988 and 1992 which of thousands of votes in his 34-year career he regretted. Interviewers even talked to teachers and coaches from grade schools Hamilton had forgotten attending. He wasn't chosen. ``I flunked somewhere, but I don't know where,'' says Hamilton, 77.

Each selection ``reflects the personality of the principal,'' says Stuart K. Spencer, campaign manager for Reagan and Gerald R. Ford. Ford was deliberative, hashing out pros and cons of each finalist with advisers night after night before deciding on Dole. Four years later, Reagan ruled out Ford after Ford gave a television interview proposing a virtual co-presidency, Spencer says. Reagan ultimately picked George H. W. Bush.

Painful Experience

Even for the chosen, the experience can be painful. In 1984, Democrats Geraldine Ferraro, 72, then a U.S. representative from New York, and Dianne Feinstein, 75, then mayor of San Francisco, were under consideration by Walter Mondale's team. Ferraro, the only woman named so far to a major-party ticket, recalls her vetting as exhaustive.

The campaign made her pay $50,000 in underpaid taxes found in an accounting error, although she said she had overpaid the same amount the previous year. Once nominated, she faced a barrage of attacks, including allegations that her husband, John Zaccaro, had ties to organized crime, which she denied.

``If God had shown me a video of the next five months of my life, I might've said, `Do me a favor, give it to Dianne,'' Ferraro says.

To contact the reporter on this story: Indira Lakshmanan in Washington at ilakshmanan@bloomberg.net

Last Updated: June 24, 2008 00:01 EDT