The governor's chief rival, Republican state Sen. Jake Knotts, told ABC News Sunday that he will pursue a criminal prosecution, even if he has to go to Washington, D.C.
That may not be necessary now with McMaster's call for an investigation.
McMaster, one of the frontrunners in South Carolina's gubernatorial 2010 race, is one of several who will be affected by the outcome of the Sanford scandal, analysts say.
McMaster is a leading contender for the governorship, along with Lt. Gov. Andre Bauer, who would take over the governor's seat if Sanford were to step down.
"If he [McMaster] has this investigation, he gets more publicity and name recognition if he does a good job," said Robert Oldendick, an executive director and professor at the University of South Carolina. "The downside is that if Sanford does leave office, and Lt. Gov. Bauer takes over, it gives him 15 to 16 months of incumbency leading into the race and that will be to his advantage in terms of media and name recognition."
Once the State Law Enforcement Division has completed the investigation into Sanford's travel funds, the attorney general's office will review it to see whether a criminal act has been committed and they can bring charges.
ABC News' Lisa Fletcher, John Hendren and The Associated Press contributed to this report.