About three in four Republican primary voters in each state say their minds are mostly made up; about a quarter could still change their minds. Eight in ten of Trump’s and Cruz’s supporters in Iowa say their support is strong. Those remaining Trump supporters who have not firmly decided are still waiting to be convinced that he can be an effective president, while Cruz supporters who have not firmly decided still want to make sure Cruz can win in November.

In Iowa, Trump has retained his own support from last month while cutting into Cruz’s edge among both tea party identifiers and evangelicals. The latter group is 38-30 for Cruz now and was 47-28 last month.

There are big differences in the rationale behind backers of Cruz and Trump: For Trump’s support the top reason is fixing the economy, and many also want to “shake up the system.” For Cruz the top reason is finding a president who will defend their religious faith. Trump leads among conservatives; Cruz leads among the smaller group that identifies as “very” conservative.