Real-estate magnate Donald Trump is the "undisputed leader" of the Republican presidential field, and his lead has grown over the past month while retired neurosurgeon Ben Carson has plummeted.Trump is the first choice of 27% of Republican primary voters nationally, according to a new survey from Quinnipiac University out Wednesday. It's his best showing in the poll since August, and a 3-point increase from last month.Carson, who was 1 point behind Trump last month, has seen his standing plunge to 16%. That puts him in a tie for third place with Sen. Ted Cruz (R-Texas).Sen. Marco Rubio (R-Florida), who along with Cruz has surged recently, found himself in second place in the poll with 17% support. Former Florida Gov. Jeb Bush (R) rounds out the top five, garnering 5% in the survey."It doesn't seem to matter what he says or who he offends, whether the facts are contested or the 'political correctness' is challenged, Donald Trump seems to be wearing Kevlar," said Tim Malloy, assistant director of the Quinnipiac Universitypoll."Dr. Ben Carson, moving to center stage just one month ago, now needs some CPR. The Doctor sinks. The Donald soars. The GOP, 11 months from the election, has to be thinking, 'This could be the guy.'"Indeed, Republican leaders seem to be increasingly bracing for the possibility that Trump could be the party's standard bearer next year. The New York Times reported Tuesday that the party is starting to become concerned that Trump could doom the GOP's down-ballot candidates if he were to win the primary contest."It would be an utter, complete and total disaster,"Sen. Lindsey Graham (R-South Carolina), a presidential rival who has repeatedly tangled with Trump, told The Times."If youre a xenophobic, race-baiting, religious bigot, youre going to have a hard time being president of the United States, and youre going to do irreparable damage to the party."Carson, meanwhile, has seen his standing tumble as he has faced a slew of controversy in recent weeks. Most recently, questions about his foreign-policy knowledge placed him under days of scrutiny.The poll found, however, that the race is still highly volatile two months away from the Iowa caucuses. Just 32% of Republican primary voters said their minds are "made up" about their voting choice, while 65% said they could change their mind.SEE ALSO:There's a problem with a common theory about Donald Trump and Ted CruzJoin the conversation about this storyNOW WATCH: Stadium security prevented one of the bombers from entering with an explosive vest, WSJ reports Click here to read full news..