Republican presidential candidate Ted Cruz dismissed attacks against his record and his personal style Monday, suggesting that his political rivals are “panicking” as the Iowa caucuses approach.

“Listen, politicians behave a certain way when they are panicking,” he told NBC in an exclusive interview aboard his campaign bus. “And they engage in attacks, they engage in personal attacks, that’s human nature. I understand that. I am not going to get drawn into that muck.”

Cruz has increasingly come under fire from fellow GOP candidates as he has risen in primary polls. On Monday, Florida Sen. Marco Rubio alluded to Cruz’s foreign policy stances, knocking “isolationist candidates more passionate about weakening our intelligence capabilities than about destroying our enemies.”