Republican Cook County Central Committee members endorsed Gov. Bruce Rauner Monday night over rival state Rep. Jeanne Ives of Wheaton.
Rauner won 27 out of 30 townships, party officials said, and clinched a majority of Chicago wards.
The decision heightens tensions between the two Republicans vying in the March 20 primary. Ives, a social conservative, has attacked Rauner as abandoning the party's traditional values while the incumbent has largely ignored the Wheaton lawmaker, focusing his criticism on J.B. Pritzker, one of six Democrats seeking the nomination.
"Ives is a strong advocate for conservative principles," said Aaron Del Mar, Cook County Republican Central Committee deputy chairman. But Rauner has greater appeal statewide, he thinks.
"He is the one candidate with the ability get elected and defeat the Democrats," Del Mar said.
An Ives ad that lambastes Rauner at what critics call the expense of transgender individuals, immigrants and women who have abortions, turned off some, Del Mar added.
"We're not in Kansas," he said. "It's not truly representative of Illinois Republican Party, we need to be the party of the big tent."
Ives has been undaunted by the loss of GOP establishment endorsements, saying some Republicans are beholden to investment banker Rauner because he has donated substantial amounts to the party. She received an endorsement from the Wheeling Township Republican organization last month.
Cook County represents the largest number of of Republicans in Illinois.