Elder McNamara was once a head paladin. He fought against the NCR at HELIOS One in the failed Operation: Sunburst and broke through the NCR lines to lead the surviving Brotherhood forces to safety. This act earned him an enormous amount of respect and loyalty from his chapter. He assumed command of the Mojave chapter, and the rank of elder, when Father Elijah vanished during the battle. He is credited with saving the Mojave chapter from complete eradication.
Fearing that the NCR would continue to hunt down the Mojave chapter, McNamara put the Hidden Valley bunker on lockdown, not allowing anyone but small scouting parties to leave, nor allowing any Brotherhood members who were outside to enter. He still fears the NCR and believes they are still hunting the Brotherhood, when in fact the NCR is currently overburdened fighting wars on multiple fronts and is not even looking for the Brotherhood. The extended lockdown and resulting attrition of the Brotherhood's sphere of influence have caused some members of the Brotherhood to question the elder's judgment, and Head Paladin Edgar Hardin is looking for a way to usurp him.
Still in the Dark: McNamara will ask the player character to do various tasks for the Brotherhood, such as looking for Brotherhood patrols, getting reports from scouts and helping repair the air filtration system by retrieving different parts from the Mojave's vaults. He can also be overthrown by Head Paladin Hardin with the help of the Courier in this quest.
Eyesight to the Blind: If not overthrown, McNamara will task the player character with planting a bug in the radio equipment at Black Mountain and to deal with the super mutants there.
Elder McNamara is described by Veronica as being one of the Brotherhood's most progressive members. He, under the appropriate circumstances, will even support the NCR. In contrast, Hardin is a conservative, dyed-in-the-wool Brotherhood member who believes in the ideals and mission of the Brotherhood without question.
In the Eyesight to the Blind quest, McNamara remarks that under his leadership, the Brotherhood has remained neutral with the neighboring Black Mountain super mutants out of respect. This runs counter to the Brotherhood's usual attitude towards mutants. However, this policy was established while Black Mountain was still under the control of the benevolent Marcus, rather than its current unstable and violent leader, Tabitha.
Even after joining the Brotherhood, McNamara will keep calling the Courier an outsider, even if he is ousted.
The following is based on unverified behind the scenes information and is speculative and may not be accurate.
McNamara is named after a fallacy known as the McNamara Fallacy. The fallacy involves making decisions by using quantitative observations and ignoring all other types of observation, as he does in the quest I Could Make You Care.
End of information based on unverified behind the scenes information.
After Elder McNamara grants you full access of the bunker, heading for his chair, if the player sits in his chair he will stop his action and stand still forever. This can be fixed by going into the console, selecting Elder McNamara with your mouse or typing prid 000e2f87, then disable, then enable. [verified]
Note: If you can't find him, type player.moveto 000e2f87 and warp to where he's stuck contemplating a wall/air vent.
McNamara may not respond at all for action/talk call. This can be fixed by loading and trying again. [verified]
After completing Still in the Dark, McNamara will be unavailable for dialogue and will indefinitely respond to attempts to speak to him with a comment stating that he is busy with efforts ending the lockdown, thus preventing the player character from finding peaceful resolutions during quests such as For the Republic, Part 2. [verification overdue]
This is likely just a minor scripting bug. Once you reach this point, exit the entire bunker complex then re-enter the bunker and talk with McNamara again. Exiting and re-entering the bunker flips a trigger switch and allows McNamara to offer you the next quest in the BoS Chain (Eyesight to the Blind) that offers you the chance to become a member of the BoS, which then allows you to ask the BoS for their support in the upcoming battle.
NOTE: You may have to wait 3 days or so after exiting the bunker complex before re-entering will work. What's happening in the meantime is the Elder is lifting the lockdown. The 3-day wait corresponds to the universal refresh time that also affects vendor inventories and non-player character respawns. However, this may still not allow the courier to initiate a conversation with the Elder.
If you have tried the above solutions and still lack results, you can open the console and enter this command: /set "000E327C".LockdownLifted to 1
On Xbox 360, it seems this may be caused by applying the 1.2 update partway through the game. Clear the update from your Xbox system cache (see Removing patches). This will fix the "lockdown bug." Go talk to McNamara, tell him about the NCR and ask him about joining the Brotherhood. You can then re-patch your game with the update after talking to him, he will remain fixed and you will be able to continue with both quests.
After attempting to receive power armor training from Elder McNamara the screen will turn black then fade back in, leaving you frozen and only able to look up and down. To fix this, try to enter console, then, selecting Elder McNamara with your mouse or typing prid 000e2f87, disable, then enable.