They have both risen to levels that aren't merited by their intelligence, competence or work ethic.

Bush got into prestigious Ivy League schools despite a poor academic record that would have disqualified other less well-connected applicants. His father got him in, where he promptly proved to be a below-average C student.
Bush then got into the Texas Air National Guard ahead of many other more qualified applicants, once again with the help of his father. He promptly followed his pattern of being an underacheiver, going AWOL and failing to complete his military committment according to credible reports.
He then went on to start up several businesses with the help of his father and father's friends. Each one failed miserably, requiring bailouts by father and friends once again. George W. Bush---consistent failure and underacheiver, put in positions of power not due to ability, but family connections.

McCain was the son of a four star admiral, as was his father. He graduated 894 out of 899 students in his class at Annapolis, a dismal academic record that should have consigned him to poor assignments in the Navy. Instead, be became a fighter pilot, promptly destroying at least 4 aircraft in the process. Implicated in the official Navy report as being a possible cause of a tragic fire that killed 130 of his shipmates on the USS Forrestal, he avoided disciplinary action only because of the actions of his admiral father, and his shootdown over North Vietnam. After his release from the prison camp, he went into politics, divorcing one wife after having an affair with a rich heiress that he later married. John McCain---consistent failure and underacheiver, put in positions of power not due to ability, but family connections.