The following graph shows real GDP quarterly (blue, annualized), and the year-over-year (YoY) change in real GDP (red).
The worst quarterly change in real GDP during the Great Recession was -8.4% annualized in Q4 2008.
Note that the tax changes at the end of 2017 had minimal impact on GDP (maybe boosted slightly), and also, as shown earlier, there was no investment boom following the tax changes.
There will be some bounce back for GDP in Q3. The worst month for economic activity was in April 2020, and the economy bounced back in May and June.