Control of the Senate hangs in the balance on Election Day. Here are key Senate races to watch

The presidential election isn't the only critical race happening on November 3. Democrats and Republicans will battle across the country over control of the Senate.

The Senate is currently split 53-47 between Republicans and Democrats. There are 35 seats up for election in the Senate, and of those, 23 belong to Republicans and 12 to Democrats. Democrats would need to win four seats for a majority, or three seats if Democrats win the White House.

There are now nine Republican-held seats rated as either leaning Democratic or toss-ups by the nonpartisan Cook Political Report, up from eight a few weeks ago.

By contrast, they list only one Democratic seat as leaning Republican, and none as a toss-up.