My ideal season finale (obviously wouldn't have worked with this season, but just generally):
Frank's approval rating is steadily dropping in the polls and he has to concede that it doesn't matter how cunning he is politically, how many favours he does or how many opponents he ruins, if he doesn't get the public on side, then it is all for naught. His supposed allies are in question and Doug Stamper's loyalty may be wavering after his breakdown and return to drinking. There is some suggestion that he may harbour ill-feelings towards Frank, and that some of his informing on the President to opposing parties may be genuine, rather than as a triple agent. At the same time, Doug can sense that the President is about to be disgraced and doesn't want him to have to go through that. It's getting close to the election and running out of options, Frank eventually comes up with a last ditch effort to swing public opinion and sympathies in his favour. He organises a special campaign address to announce his plan, hoping for as big a crowd as possible. Although she was originally unable to attend, Claire manages to reorganise her schedule last minute, so that she can stand beside him during the speech. She arrives, to Frank's surprise, just as he is about to step up to the lectern. Frank gives the beginning of a rousing speech, but about a minute into it, a gunshot rings out. It appears to have missed and hit the lectern instead. Meechum dives in front of Frank and takes the second shot in the centre of his back. Frank sees that Meechum is dead, as the other bodyguards try to rush him off the stage. He then looks around and notices the red seeping through on the stomach of Claire's dress. The first shot ricocheted oddly off of the lectern and hit her. She collapses.
First episode of the next season:
A few days before the speech, Frank goes through the motions of the day-to-day leading up to the speech. Some of the other staff are suspicious that Doug is up to something and have evidence that he is leaking intelligence. Later, he cannot be reached for a number of days. He is not at home and Claire is worried he has fallen off the wagon again. Various parties express open hostilities towards the President and tensions are high. A few minutes before he is about to give his speech, Frank puts on a bulletproof vest. We see the events of the presidential address from the gunman's perspective. Getting into position, looking through the sights etc. Frank gets a minute into his speech and the gunman fires. The bullet richochets off the lectern and hits Claire. Meechum dives in front of the President and the gunman fires again and hits Meechum in the back, killing him. Frank is dragged off stage as Claire collapses. We see that the gunman is Doug Stamper.
Cut to a week before the speech
Frank considers his dire situation and ever-dropping approval rating. He comes up with a plan. He meets secretly with Doug who is eager to prove his loyalty. Frank explains the idea that an assassination attempt on his life will get the public on his side and hopefully their sympathy will get him the backing he needs to win the election. Knowing that the lectern is bulletproof, he tells Doug to wait for him to reach a specific keyword in his speech and that is the cue to fire a shot into the lectern, as if he missed. Then knowing that one of the bodyguards will dive in front of the President, Doug is to wait until they do and then fire again. There has to be a sacrifice, so that there can be a hero. Even if the supposed assassination attempt is unsuccessful, it can't be bloodless, and the bullets have to be live rounds, not blanks, or it won't be convincing and someone might find out it was staged. Frank will be wearing a bulletproof just in case. Doug calls the plan reckless and asks why he should be the one to do it and Frank explains he is the only one he trusts with his life. Frank doesn't tell Claire about the plan and organises for the speech to happen at a time when she can't be there, so that she doesn't have to see it, but she manages to come anyway without him knowing or being in a postion to call it off. The first bullet ricochets unexpectedly and hits her. Frank wins the election, but possibly only because Claire was unintentionally injured. The plan itself may not have been enough. Claire survives, but eventually Frank has to admit the plan to her, which is the seeds for her eventually turning against him fully and his downfall.
