Exactly and recent history proves that. This election is a referendum on Trump and his childish antics and very unpresidential behavior. If the people give complete control to the Democrats, it won't be a mandate or they actually want the democrats in control or approve of their policies. It will be because they want Trump gone.
History, 1994, Bill Clinton president, Democrats in full control of congress, lost congress. 2006, Bush president, Republicans in full control of congress, the GOP lost congress. 2010 Obama president, Democrats in full control of congress, the democrats lost the house, then in 2014 the senate. 2018, Trump president, Republicans in full control of congress, the GOP lost the House and it seems will lose the presidency and the senate this year if things continue as they are today. A mighty big if.
Now I must repeat this, if the Democrats gain full control it won't be because the people like the Democrats more than the Republicans or want them in full charge. It will be they absolutely want Trump gone and the Democrats are the lesser of two evils, a tool to be utilized to get rid of Trump. If the Democrats take this as a mandate or approval of themselves by the people and over react, they'll lose the House in 2022. Write that down.