The last polls out of Iowa show Trump getting around half the vote with Nikki Haley at 20%, Ron DeSantis at 16% and everyone else down in Chris Christie territory. I suspect this is not an indication of how much G.O.P. Republicans love Trump but of how much those who want a Republican in the White House don't see any credible alternative. And I recall some pundit somewhere saying that early primaries and caucuses like this don't have much to do with who'll get the nomination but a lot to do with whose donors will stop donating.
What's happening on the ground in Iowa? I don't know how important it is in the big picture but this article by Lisa Lerer discusses how it is there right now.