Trump county-level vote roughly in line with combined vote of Trump and Ted Cruz in 2016
In 2016, Trump finished a close second in Iowa with 24 percent of the vote, trailing Cruz's 28 percent. But since then, Trump has won over much of the very conservative and more religious voter base that backed Cruz while holding onto the more populist parts of the party. Understandably then, we see a fair bit of alignment with tonight's vote and how Trump and Cruz performed combined at the county level in 2016. Based on 27 counties where we have at last 85 percent of the expected vote, there's a fairly strong correlation of 0.72 between Trump's vote tonight and the Trump+Cruz 2016 caucus showing.
Correlation isn't causation, but we can see in the preliminary entrance poll data how Trump has captured much of the Cruz wing of the GOP. Among voters who identified as "very conservative," who made up half of the electorate, Trump won 60 percent. In 2016, Cruz won 44 percent of the vote among very conservative voters in a more crowded race, while Trump only won 21 percent.
—Geoffrey Skelley, 538