So, since 1952 Party Nominees for President have been getting National Security briefings to prepare them for the possibility of getting the job. (note that this is practice, not law)
Access to classified information, in all cases, requires a Security Clearance appropriate to the classification level of the information involved. Presumably, the National Security information given to a Presidential Nominee will be at least Secret, and likely Top Secret.
Can Donald Trump qualify for a Top Secret clearance?
The most concise explanation I found in a cursory search of what’s involved comes from the FBI relating to clearances for Law Enforcement personnel:
www.fbi.gov/…
Q: What kind of inquiries will the FBI make into my background?
A: Credit and criminal history checks will be conducted on all applicants. For a Top Secret security clearance, the background investigation includes additional record checks which can verify citizenship for the applicant and family members, verification of birth, education, employment history, and military history. Additionally, interviews will be conducted of persons who know the candidate, and of any spouse divorced within the past ten years. Additional interviews will be conducted, as needed, to resolve any inconsistencies. Residences will be confirmed, neighbors interviewed, and public records queried for information about bankruptcies, divorces, and criminal or civil litigation. The background investigation may be expanded if an applicant has resided abroad, or has a history of mental disorders, or drug or alcohol abuse. A personal interview will be conducted of the candidate.
Being a long-time blow-hard is not an official criteria, but should be.
Can Donald Trump legitimately be issued a Security Clearance? Personally, I’m doubtful.
Should President Obama suspend tradition and refuse to brief either Nominee? Hillary really doesn’t need to be brought up to speed, and Trump really can’t be trusted not to blurt out something damaging during a tantrum.