Iowa has always been unpredictable and the winner of the Caucus has not always been the national front runner.
Back in 1980. George H.W. Bush upset national front runner Ronald Reagan in the Iowa caucus for example.
Iowa Caucus https://en.wikipedia.org/wiki/Iowa_caucuses
2012 - Rick Santorum (25%), Mitt Romney (25%),
2008 Mike Huckabee (34%), Mitt Romney (25%),
2004 - GW Bush unopposed
2000 George W. Bush (41%), Steve Forbes (31%),
1996 Bob Dole (26%), Pat Buchanan (23%),
1992 George H. W. Bush (unopposed)
1988 Bob Dole (37%), Pat Robertson (25%), George H. W. Bush (19%),
1984 Ronald Reagan (unopposed)
1980 George H. W. Bush (32%), Ronald Reagan (30%),
1976 Gerald Ford (45%) and Ronald Reagan (43%)
And thank GOD, that Reagan prevailed!