"They ask everything from your tax records to your college transcripts to your SAT scores," Zengerle said Tuesday on "CBS This Morning." But he noted that what "gets really uncomfortable is some of the personal questions."
He mentions a few: Have you been unfaithful to your wife? Have you ever paid for sex? Are there any sex tapes? "Even though I could answer all these questions quite comfortably it was still uncomfortable being asked them," he said.
Zengerle said a vice presidential contender undergoes the most intense scrutiny of any politician. "The presidential candidate manages to avoid this process. It's the vice presidential candidate that goes through it."
He said the vetting process is so rigorous because the presidential campaign doesn't want to be taken aback by the unknown. "They want to know everything there is to know so when it does come out they want to be prepared how to respond," he said.
As for the vetting process of Sarah Palin, Sen. John McCain's running mate in 2008, Zengerle said they did a thorough vetting and were fully aware of Bristol Palin's pregnancy and other potential problems, but the campaign still chose her because they believed, "high risk, high reward."
Although little is known about Mitt Romney's vetting process, he suspects that Palin's lack of knowledge about foreign affairs possibly prompted a current events test this time out.
He noted that the vetting process changes after every campaign to avoid the mistakes that were made. "It's a damage control process. You're not necessarily picking a (presidential) candidate based on the vice presidential choice, but if you pick a terrible vice presidential candidate, that could harm you. Sarah Palin is the cautionary tale there," Zengerle said.