(CNN) – Newt Gingrich is edging out his rivals for the Republican presidential nomination in Mississippi, according to a new poll. The American Research Group survey of likely Republican primary voters released Friday showed Gingrich with 35% support, followed by Mitt Romney with 31%, Rick Santorum with 20% and Ron Paul with 7%. Gingrich's margin over Romney increased slightly among those who said they will definitely vote in the March 13 primary, 37% to 30%. Santorum garnered 17% support and Paul received 5% among the same group. The poll was conducted after Super Tuesday, when each of the GOP White...