The immigration debate between Sens. Marco Rubio of Florida and Ted Cruz of Texas has touched off a full-blown war of words on the campaign trail.
"Immigration is an issue which is near and dear to the heart of most of the Republican electorate and what Cruz and Rubio realize is they've got to knock each other off for the potential to face Trump," said GOP strategist Ford O'Connell, who is not affiliated with any of the 2016 candidates.
The battle lines have been drawn.
"What Cruz wants to do is to slime Rubio as an establishment RINO before Rubio can gain any momentum in New Hampshire." ("RINO" stands for "Republican in name only, a contemptuous term the most conservative Republicans use to describe their more moderate counterparts.)
Cruz's weapon of choice is what conservatives refer to as "amnesty," a path to citizenship.
"What Rubio's doing...by going after Cruz on this issue is to say, 'Wait a minute, you've portrayed yourself as a straight talker and you're lying through your teeth,'" O'Connell told CBS News.