Eehh.. Even if the dems get control of all 3 houses, which is very possible, nothing will change. The dems will do nothing substantive with their power, and the pendulum will swing the other way in the mid-terms.
look for exciting legislation like “the green new deal of tax credits!” and “the President must release his tax returns bill!”.
only way the dems hold onto the hypothetical power is if there is somehow a massive covid breakthrough while Joe is in office. If thats the case he will automatically get credit for it.