Des Moines, Iowa (CNN) Wisconsin Gov. Scott Walker can't escape the divisive battles with union workers that have defined his tenure as governor -- not even in Iowa.

The Republican presidential candidate faced boos and chants of "liar" from dozens of protesters who drove down from Wisconsin as he stumped Monday at the Iowa State Fair Des Moines Register soapbox, and the heated incident devolved into physical altercations between supporters and demonstrators.

As the protesters shouted, Walker seized the opportunity to highlight his record as a fighter who faced off against unions in Wisconsin and became the first governor to successfully fight an effort to recall him from office.

"I am not intimidated by you sir or anyone out there," Walker said to one heckler. "This is what happened in Wisconsin. We will not back down, we will do what is necessary."

Protestors interrupt @ScottWalker - "I am not intimidated," he says pic.twitter.com/bFRc8uNSl0 — Betsy Klein (@betsy_klein) August 17, 2015

Walker's affiliated super PAC is named "Unintimidated PAC" -- a nod to his successful fights with organized labor since taking office in 2011, including surviving a recall election.

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