Sens. Ted Cruz and Marco Rubio have been sparring over national security and immigration policy as their rivalry intensifies in the Republican presidential primary race.

Republican presidential candidates U.S. Sen. Marco Rubio (R-FL), U.S. Sen. Ted Cruz (R-TX) and Ben Carson on September 16, 2015. (Photo by Justin Sullivan/Getty Images)

Now their conflict is moving to Iowa and a powerful evangelical constituency that Rubio is making a play for months after rivals sank roots.

Cruz and Rubio will appear today with a group of candidates at a forum hosted by a prominent Iowa Christian organization.

Cruz has spent more time than Rubio in the state and has built a deep organization with endorsements from state and local officials.

Also on stage will be retired neurosurgeon Ben Carson, who has led some recent Iowa polls and has a strong evangelical following.