At that point the market began to factor in deregulation, etc.
I'm no fan of Trump or the tax cut but 3 things Trump has done right, IMO: deregulation (which has boosted the economy), Supreme Court nominations, and China trade, which has hurt the economy in the short run but is essential for the longer term.
Now if he had better deportment, wasn't so crude, ill mannered, and so biased to favor the rich and his friends and family.
You have one thing right though, the tax cut was awful, especially the estate tax cut to benefit only the rich. BTW, Obama hypocritically also lowered the estate tax for the super rich. Obama actually went farther than Trump did in that regard. Trump simply raised the exemption amount, Obama lowered the estate tax rate for billionaires. It's a scandal.