Republican Rep. Todd Rokita saw a spike in contributions after he took up legislation to end employee protections for tribal casino workers.
Braun is pouring roughly $800,000 of his own money into his campaign.
Both Donnelly and Rokita accuse the other of politicizing the situation.
Rep. Rokita declined to come to the group's town hall meeting after they tried many times to invite him.
Republican Secretary of State candidate Charlie White is facing questions about his voter registration.