Whoever is the president next year may have the ability to appoint one or more justices to the US Supreme Court. But to get those justices confirmed, the president will need the US Senate behind him. To gain Senate control from Republicans in November’s elections, Democrats will need a net gain of three seats (if former Vice President Joe Biden holds onto his lead over President Donald Trump and claims victory) or four seats (if Trump wins).
An early look at the data finds that Democrats are the slightest of favorites to take back the Senate. The chance Democrats net gain at least 3 seats is about 3-in-5 (60%), while the chance they net gain at least 4 seats is about 1-in-2 (50%). There is still a lot of uncertainty. Democrats could realistically end up anywhere from a net loss of 4 seats to a net gain of 11 seats, though a few more times than not, they’ll end up in the majority.
Hit the link for more on the probabilities.