We cant' afford to take the chance of another 4 yrs. of trump.
First of all, it takes time for us to see the effects of policy changes. Blame/credit does not shift overnight inauguration day.
Obama inherited an economy crashing into deep recession. When he checked out, America was enjoying it's 75th consecutive month of job growth, unemployment had shrunk f/ 10.2 to 4.8, the stock market nearly tripled etc. He did that despite the GOP vow to obstruct him, top priority to make him a 1-term president as America inaugurated the first Afro-American president and proof of their intentions by how they shattered the filibuster record.
Trump had the luxury of inheriting an economy blossoming in recovery. Trump did nothing significant about the economy in 2017 but he didn't hesitate to take credit for Obama's work. Trump's policy changes on the economy begin in 2018 w/ tax reform that doubled the deficit and starting a trade war. The ball is officially in his court now.
If the effects f/ the poor gwb decisions (or lack thereof) had been felt sooner, he would never have been reelected. He checked out w/ one of the lowest approval ratings in history. Rep presidential nominee McCain didn't want his endorsement ... lol (unprecedented).