Democrats need a net gain of four Senate seats to win the majority outright. If Joe Biden wins, Democrats would need just three seats, as Kamala Harris, as vice president, would cast the tiebreaking vote in the Senate.

Republicans would need to pick up 21 seats, but it’s thought very unlikely they will be able to do that.

Arizona, Georgia, Iowa, Michigan, Nevada, North Carolina, Ohio, Texas, and Wisconsin will all be important to watch. But perhaps the most important state to watch will be Florida. If Biden wins there, it’s pretty likely he’ll win the election; there are few paths to victory for Trump that don’t run through the state. If Trump wins Florida, Biden could still win the election. Pennsylvania is one to watch closely, too, but it’s unlikely to have final results for days.

Due to the pandemic, a lot of people are voting by mail, which means the race will have to be a blowout to be called election day. Otherwise, vote-counting could take days or weeks, particularly if close races are contested in the courts. One thing to keep in mind about early results: In many states, in-person votes will be counted more quickly than mail-in ballots, which could result in it looking like Trump is leading early on, but once absentee ballots have been counted, Biden could seriously cut into or overcome Trump’s lead.