Romney had addressed most of the concerns of the people. When an airplane is about to leave the ground, the crew goes through a process of checking to see if they had done everything necessary for the airplane to fly and that all of the mechanical features of the airplane are functioning correctly. They have a list and they check off (or, tick off) everything on the list - they make a mark with a pencil or pen after each item on the list. The writer here is saying that Romney has essential done the same thing - he talked about: the economy (check), war (check), taxes (check), and so on.
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