Yes, I was puzzled by where Quinn appeared from, when Carrie was wandering noisily around the house by herself -- pretty odd not to notice Woolly Hat wasn't with the others, and pretty risky as Carrie could easily have been killed by the time he reappeared. The bomb doesn't make a lot of sense to me either.
And as others have said, wouldn't there be better people to frame for the PE's assassination than Quinn, a veteran whose PSTD is well-documented, and whose service to US security is long and exemplary, and has resulted in a visible disability? (Or is his past so Black Ops that his record is entirely unofficial?) Especially when the anti-Keane faction are so exercised by her 'cowardly' soldier son's last moments. Or is that the point - a disabled. traumatised veteran, outraged by 'lies' from the PE and her son's military award, is driven beyond endurance and kills her?
I think Quinn will die protecting the PE in the final episode -- not sure from what, exactly. Given all the references to waiting for reinforcements, surely that's a false trail - it's such a hoary thriller cliché for the cops/security guards/army to turn out to be the bad guys? Might there be another bomb?
I think the whole point of this season was to try (belatedly) to address the accusations of Homeland's Islampohobia by showing a Muslim American suicide bomber turn out to be innocent and framed, and the real villains to be deep inside the US political establishment. I agree with other people that Dar is going to turn out to be a comparatively small fish in the anti-Keane faction, and I don't think he is colluding with/in the know about the assassination plan, I think he was just happy to smear her and wreck her credibility/get her impeached.