Gore lost a very close election (537 votes in Florida), under circumstances that have been unfavorable in the last sixty+ years (trying to win a third term in the White House for a party.)
There are several measures of legal standards. It's much easier to get a grand jury to agree to go forward on a case than it to get a regular jury to determine beyond reasonable doubt that a crime was committed.
Any questions the potential prosecutors have are questions that any half-decent lawyer would be able to exploit.