Wisconsin Gov. Scott Walker continues to hold the top spot among likely participants in Iowa’s Republicans Caucus, but his support is shrinking as other top contenders duke it out for second place, according to a new Quinnipiac University poll released Wednesday.

Walker currently has 18 percent of the vote, leading the rest of the declared and likely Republican presidential contenders. The new numbers amount to a decline compared to prior Quinnipiac polls In February Walker boasted 25 percent of the vote, inn May 21 percent.

With Walker on top, two non-politicians are tied for second place — businessman Donald Trump and neurosurgeon Ben Carson both received 10 percent of the vote. In May’s Quinnipiac Iowa poll Carson had seven percent of the vote and Trump was not included.

Rounding out the field are Sen. Rand Paul (R-KY) and Sen. Ted Cruz (R-TX) each with 9 percent. Former Florida Gov. Jeb Bush has 8 percent, Sen. Marco Rubio (R-FL) with 7 percent, and former Arkansas Gov. Mike Huckabee has 5 percent. Five percent were undecided and no other candidate received above four percent. New Jersey Gov. Chris Christie was at the very bottom of the poll with 1 percent.

Peter A. Brown, assistant director of the Quinnipiac University Poll noted that while Walker remains in front, new candidates entering the stage have made the race more “muddled.”

“In that second-place gaggle is newly declared candidate and billionaire businessman Donald Trump, whose early showing – he is getting one in 10 votes – worries many party leaders. They see him as a potentially disruptive force,” Brown said in a statement. “Gov. Jeb Bush’s formal announcement seems to have inched up his standing, while New Jersey Gov. Christopher Christie may think making his candidacy official will help him climb out of the caucus basement.

In terms of favorability — or lack thereof — Trump and Bush received the most negative reviews with 28 percent saying they would definitely not support Trump and 24 percent said not support Bush. Christie came in third in the negativity rating with 18 percent.

“Meanwhile, the candidate other than Walker with the best favorability rating is surgeon and political neophyte Ben Carson,” Brown noted. Carson currently has a favorability rating of 63 percent. Walker’s is 66 percent. Just 7 percent view Carson unfavorably, and 8 percent view Walker unfavorably.

The new poll was conducted from June 20-29 among 666 likely Iowa Republican Caucus participants and has a margin of error of +/-3.8 percentage points.