Walker, who is expected to make Iowa the centerpiece of his early campaign efforts after he officially joins the presidential field on July 13, has the support of 18 percent of likely GOP caucus participants, according to the Quinnipiac University poll.

That puts him ahead of a crowded Republican field, though his support is slipping. The decrease from the previous poll — Walker was at 21 percent two months ago — is not statistically significant. But his decline is more pronounced from a Quinnipiac poll in February of this year, in which Walker led the next-closest competitor with a quarter of the vote.

The candidates finishing behind Walker are tightly bunched together: First-time candidates Ben Carson and Donald Trump tie for second place, with 10 percent of the vote. Just 1 point behind are Sens. Ted Cruz (Texas) and Rand Paul (Ky.). Former Florida Gov. Jeb Bush is at 8 percent, and Florida Sen. Marco Rubio is at 7 percent.

Former Arkansas Gov. Mike Huckabee, who won the 2008 Iowa caucuses, is at 5 percent, followed closely at 4 percent by former Texas Gov. Rick Perry and former Pennsylvania Sen. Rick Santorum, who won the 2012 caucuses. Former Hewlett-Packard CEO Carly Fiorina is at 3 percent, joined by Louisiana Gov. Bobby Jindal, who entered the race last week, while the poll was in the field.

Ohio Gov. John Kasich, who is expected to enter the race on July 21, is at 2 percent. New Jersey Gov. Chris Christie declared his candidacy on Tuesday, and he earns just 1 percent of the vote (the poll was conducted entirely before his announcement). South Carolina Sen. Lindsey Graham is also at 1 percent. Former New York Gov. George Pataki was offered to the 666 likely caucus-goers who responded to the poll as an option, but he drew no support.

Walker continues to run best among conservative caucus-goers, though the poll indicates he appeals to other segments of the likely electorate, too. He wins 21 percent of caucus-goers who say they’re “very conservative,” but he also captures 18 percent of “somewhat conservative” and 12 percent of “moderate” or “liberal” voters.

Other candidates have more focused support. Bush wins just 3 percent of “very conservative” voters. Cruz is second among very conservative and tea party caucus-goers but earns little support among those outside those categories.

Walker’s dip at the top actually comes as he’s become better-known — and better-liked. In the new survey, 66 percent of likely caucus-goers have a favorable opinion of him, up from 59 percent in late April and early May, and 57 percent in February. Meanwhile, the percentage who view him unfavorably hasn’t ticked up at all and now sits at just 8 percent. A little over a quarter of caucus-goers said they have no opinion.

The candidate with the second-best image rating is political neophyte Carson, the former neurosurgeon. Sixty-three percent of caucus-goers view him favorably, and just 7 percent have an unfavorable opinion. Three in 10 voters have no opinion.

Three GOP hopefuls are viewed more unfavorably that favorably by likely caucus-goers: Trump (42 percent favorable/47 percent unfavorable), Graham (20 percent/38 percent) and Christie (25 percent/59 percent) — whose woeful numbers in the new survey jibe with the governor’s exclusive focus on New Hampshire, not Iowa, in the days following his campaign rollout.

Bush has seen a slight uptick in his favorability numbers: He was underwater in the previous survey two months ago, but in the new poll, 46 percent have a favorable opinion, and 42 percent have an unfavorable one.

But Bush still faces resistance among the most conservative caucus-goers: Even with Trump in the race, roughly a quarter continue to say that Bush is the one candidate they definitely would not support — including 37 percent of self-identified tea party supporters.

The poll was conducted June 20-29, and results for likely GOP caucus-goers carry a margin of error of plus or minus 3.8 percentage points.