Kennedy's candidacy was, in my opinion, fatally flawed from the beginning. Not only was the cloud of Chappaquiddick hanging over everything, but Kennedy was unable to articulate a reason for running, a sad fact that is literally true; he was asked the question during an interview with CBS' Roger Mudd and could not answer the question. While there was a "rally 'round the flag" effect that benefited Carter due to the Iranian hostage crisis, it is still very difficult to defeat an incumbent President in a primary, even for a Kennedy. Ted Kennedy was a great US Senator (IMO), but he was a lousy presidential candidate. Kennedy did benefit from liberal dissatisfaction with Carter, but in the Democratic party of 1980, that doesn't get one as far as it would today. One might have seen a closer race without Iran, but even with the rotten economy (and it truly was awful then), Kennedy was running as a classic liberal in a year where the New Deal coalition was on the brink of extinction. Moreover, if you look at the states where Carter won, they are basically states he would have won under any circumstances -- Southern and border states and a few industrial states like Ohio and Illinois. Kennedy actually won the bigger states like New York, Pennsylvania and California. Using 1980 delegate math, Kennedy did about as well as one would expect running against a Southern moderate who had overwhelming Southern support. So, with all this in mind, I think Carter would still win. It might be closer than it was, but to change the outcome, you need Ted Kennedy to be a far better candidate than he was.