For the Republic, Part 2: There is a way to oust McNamara and have a peaceful outcome. However, once you talk to Hardin and begin the process of overthrowing McNamara, you just simply don't go back to the BoS bunker until you've talked to Moore about the Brotherhood. Hardin doesn't "officially" become Elder until you return to the bunker.
When Veronica Santangelo is in your party, Hardin will tell Veronica that "it's dangerous outside" and that he "hopes she's been practicing her drills."
Veronica mentions that Hardin taught her how to box when all the other Paladins refused.
During her quest, I Could Make You Care, Veronica describes Hardin as an unyielding man who would charge her with sedition if she continued to push her ideas of getting the Brotherhood to change its course.
If Hardin is to become Elder, the optional objectives of the quest Still in the Dark must be completed.
If Hardin has become Elder and the player wishes to remain peaceful with the Brotherhood of Steel, he can skip the part of the quest using the console command SetObjectiveDisplayed 00136166 55 1 (Brotherhood eliminated) or SetObjectiveDisplayed 00136166 56 1 (Brotherhood agrees to ally with the NCR) and simply talk to Colonel Moore for the next part of the quest.