31.0% Ted Cruz24.4% Donald Trump
12.3% Marco Rubio
5.8% Ben Carson
4.6% Jeb Bush
48.5% Hillary Clinton42.3% Bernie Sanders
4.6% Martin O'Malley
This survey of 1,007 likely Iowa caucus voters was conducted by telephone from January 4, 2016 through January 8, 2016.
By design, half of the respondents consist of likely Democratic caucus attendees (503) and half consist of likely Republican caucus attendees (504). The margin of error for the full sample of 1,007 is +/- 3.1%, while the margin of error for each subgroup by party (Republican caucus voters or Democratic caucus voters) is +/- 4.5%.
http://www.aarp.org/research/topics/economics/info-2015/ia-likely-primary-voters-social-security.html