katieb93, i wouldn't. what's your end goal for the PhD - academia? If so, multiple thousands in loans isn't a good move. the market is tight and it will take forever to pay off (not sure how grand Pitt's placement record is either?)
if you're interested in security studies generally, i'd really recommend working at a D.C. think tank. you get the equivalent research/writing experience to a second masters, but with the benefit of publishing in unique places. and! you get paid. ISW tends to to cycle through russia experts with relative speed - maybe worth a look?