The GOPe already took out Walker quite handily, in case you have amnesia.
Trump took Walker out.
On June 30th, Walker was at 18.3% in Iowa, about 9 points ahead of Rubio, Huckabee, and Paul. Trump, who had joined the race on June 16th, was in 9th place, about 4.5%, behind Rick Santorum.
On July 31st, Walker was at 19.7% ahead of Trump, who was in second place at 13.3%.
On August 6th, the day of the first political debate, Trump had taken the lead at 20.3% to Walker’s 18.7%.
Walker had positioned himself as a D.C. outsider, but Trump took that position away from him (very effectively) at the debate.
A week later, on August 13th, Walker had slid to third place at 11% behind Trump at 19.3% and Carson at 11.7%.
By September 1st, Walker had slid behind Cruz into 4th place.
In none of the above, were any of the GOPe involved in taking out Walker. Trump, Carson and Cruz had taken down the Iowa front runner, and if Trump had not grabbed the lead, Walker would likely have not collapsed like he did.