Posted this before, but here is some insight into how election fraud is remediated:

when the tainted votes cannot be specifically identified, as is often the case, the proper remedy is less clear. Nevertheless, when the number of tainted votes exceeds the margin of victory, most courts have a comparatively easy time resolving the contest if the ostensible victor of the election is demonstrated to be the intended beneficiary of vote fraud. In such a circumstance, courts will often presume that all of the illegal votes favored the victor (even if the votes cannot be specifically identified) and will deduct that number of votes from the official tally, thereby reversing the outcome.

Courts face a more difficult question when the total number of votes demonstrated to have been tainted by fraud or misconduct is less than the margin of victory but when the fraud may have extended to additional votes. In some such instances, courts have merely voided the election

http://www.electionlawissues.org/__data/assets/pdf_file/0020/6923/huefner.pdf