He added, “All the opposition research will have been done for Joe Donnelly at that point.”

Mr. Rokita said he had no concerns that the attacks would help the incumbent Democrat. “I think this primary is very cleansing,” he said. “I want voters to know about these two guys. And I want them to know about me.”

Referring to two previous Republican presidential candidates, John R. Kasich and Mitt Romney, Mr. Rokita added: “Messer at this point is like all losing candidates, like Kasich or Romney, ‘if you beat up on me, we are all going to lose.’ Absolutely wrong. I am not waiting for Joe Donnelly to stick a knife in Luke Messer or Mike Braun in November. I am getting it all out now. Because Donnelly will stick in a knife in them.”

That kind of language has prompted concern among some of the state’s most influential Republicans.

Mr. Grand, who supports Mr. Messer, was particularly critical of Mr. Rokita trying to claim a populist mantle by deriding so-called elites. Mr. Rokita’s “elites” are something else to Mr. Grand: “People that know what’s good for the Republican Party, yes, longstanding Republicans, yes. People who know how to elect Republican candidates.”

“Or,” he asked, does Mr. Rokita “want to go back to the group that gave us Mourdock?”

That was a reference to Richard E. Mourdock, a candidate whose backing from Tea Party groups and national conservative organizations six years ago led to the defeat of a longtime incumbent Republican, Senator Richard G. Lugar, in the Indiana primary. Mr. Mourdock went on to lose to Mr. Donnelly.

Mr. Mourdock painted Mr. Lugar as out of touch with the state, and emphasized the fact that he lived in Virginia, a theme that Mr. Rokita has reprised against Mr. Messer. He has also made an issue of the fact that Mr. Messer’s wife, a lawyer, is on the payroll of an Indianapolis suburb even though she, too, lives in Virginia.

Mr. Messer, the father of two teenage daughters, said he was raised by a single parent and felt it important to be closer to his children, and said voters would understand.