There are quite a number of good articles on the subject if you want a thorough answer, but some of the main things are:
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He's responsible for a massive deregulation of financial institutions that were a precursor to the Wall Street issues that led to the giant government bailout.
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He pushed "trickle down economics," which is the theory that if you cut taxes on corporations and the wealthy, they'll succeed more and create more jobs so that everyone wins. This is something conservatives always push and it's always a horrible failure that results in a bigger and bigger income gap.
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He funded his big tax cuts (mostly for the wealthy) by slashing federal assistance programs, including low income housing subsidies and mental health support, resulting in an unprecedented surge in homelessness that we're still wrestling with today.
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Nancy Reagan was the "Just say no to drugs" lady - the figurehead of the largely failed war on drugs which was like trying to prevent teen pregnancy with an abstinence only education program.
There's a lot more, but those are some of the big ticket items.