Beating Trump in 2020 will not be easy, but it will be simple.
Why won't it be easy? He'll be the incumbent, and has already proven to have better political instincts and ability to reach swing voters in swing states better than our party's political class does. He'll have the full array of rightwing media on his side, and the mainstream press will suck up to him. Plus, he'll have state GOP and the DOJ conspiring to make it harder for minorities to vote.
But, beating him will be simple enough: attack his strengths, i.e. why the non-racist swing voters decided to vote for him. Attack him for not bringing real change. Attack him for failed leadership. Attack him for corruption in office. Attack him for cozying up to the billionaires and the cutting their taxes. Attack him for making the economy worse. Attack him for the US being a less respected and less safe country.
Those are the issues where he'll be vulnerable--where he made promises he won't be keeping.