Editor's note: Ruben Navarrette Jr. is a CNN.com contributor and a nationally syndicated columnist.
By Ruben Navarrette Jr., CNN Contributor
San Diego (CNN) - In a popular fable, a scorpion asks a frog to carry him across a river. The frog resists at first, afraid that the scorpion will sting him. The scorpion points out that - as a practical matter - if he stings the frog, they both die. The frog gives in. Halfway across, the scorpion does in fact sting the frog and they both drown. Why would the scorpion do that, the frog asks. The scorpion responds that he can't help it, that this is his nature.
The moral: Some creatures can't control their natural impulses, even if it would lead to their own demise.
It's the same way with Republicans when they discuss immigration, as the four remaining GOP presidential hopefuls did Wednesday night during the CNN debate in Mesa, Arizona.