They don't even know.
Sure it's about repealing Obamacare because they've convinced their base that it's worse than a thousand Hitlers. Sure they always want to find ways to give more money to rich people. But in this particular context they have no idea what they're doing.
Some of them would, of course, abolish Social Security and Medicare if they were your malevolent dictators, but they aren't you malevolent dictators. They need to win elections, and increasingly they need to win elections by pandering to people who receive and like Social Security and Medicare.