Claire McCaskill is a Democrat who represents Missouri. She's running against Missouri Attorney General Josh Hawley. McCaskill has been a member of the Senate since 2006. This race is predicted to be extremely close — based on recent polling, the New York Times currently has the Missouri senate race labeled a tossup.

Dianne Feinstein is the senior senator from California, which she's represented in the Senate since being elected in 1992. Feinstein is running against another Democrat, Kevin de León, because of the state's primary system, as GQ reported. So the seat is almost assuredly going to stay in the hands of the Democrats.

Dean Heller is a Republican who has represented Nevada in the Senate since 2011. Heller is running against Rep. Jacky Rosen, who was elected to Congress in 2016, Vox reported. This is another close race — it too is labeled a tossup by the New York Times.

Joe Donnelly is a Democrat who represents Indiana. He was first elected to the Senate in 2012. Donnelly is in a tough race in Vice President Mike Pence's home state, where he's running against state Rep. Mike Braun, as the previously-mentioned article for GQ noted. It could go either way.

Bill Nelson has been representing Florida as a Democrat in the Senate since 2000. He's running against Rick Scott, the state's Republican governor. Florida's race is also labeled as a tossup by the New York Times.

Chris Murphy is Connecticut's junior senator. He's a Democrat who was elected in 2012. Murphy is running against Matthew Corey, but it's likely that Murphy will keep his seat, as the New York Times noted on its interactive elections page.

Heidi Heitkamp is a Democrat in a red state and cast a vote against Kavanaugh during his confirmation hearing, as CNN reported. According to her Senate website, Heitkamp is North Dakota's first female senator. That being said, she's in a really tough race. The Cook Political Report has the North Dakota Senate race labeled as a tossup.

Joe Manchin is another Democrat in a red state. He's represented West Virginia in the Senate since 2010. Unlike Heitkamp, however, Manchin voted in favor of confirming Kavanaugh. The Cook Political Report currently has the West Virginia race labeled as Leaning Democratic, but it remains to be seen what will happen when West Virginians vote in November.

Jon Tester is a Democrat representing Montana. Tester was first elected in 2006. Tester is running against Republican Matt Rosendale in a tight race, as Politico noted. The Cook Political Report has this race marked as a tossup, while the New York Times has it labeled as leaning Tester's way.

Mazie Hirono is a Democrat. She's represented Hawaii as a senator since 2012. It's pretty likely that Hirono will win another term, according to the Cook Political Report.

Tammy Baldwin is a Democrat representing Wisconsin. According to her Senate website, when she was elected in 2012, she became Wisconsin's first woman senator, as well as the first openly gay senator. Baldwin is running against Leah Vukmir, a state senator, as the previously-mentioned article from GQ noted, but the Cook Political Report currently has Wisconsin's race listed as a "likely" win for Baldwin.

Tina Smith was selected to fill former senator Al Franken's position after Franken resigned due to allegations of sexual misconduct. Smith is a Democrat and was previously Minnesota's lieutenant governor, but her re-election isn't certain. Both the Cook Political Report and the New York Times listed the race as only "leaning" Smith's way.

Yep, both Minnesota senators are up for re-election in 2018. Amy Klobuchar is a Democrat who was first elected in 2006. According to her Senate website, she's the first female senator to represent Minnesota. Klobuchar is very likely to win her race, according to the Cook Political Report.

Ted Cruz is the junior senator representing Texas and was first elected to the Senate in 2012. He's in for a fight against the Democratic candidate, Rep. Beto O'Rourke, however. The Cook Political Report has this race listed as a tossup.

Roger Wicker is a Republican representing Mississippi. He's been a senator since December 2007. It's highly likely that Wicker will win his re-election bid, as the Cook Political Report noted.

Sherrod Brown is a Democrat representing Ohio. He was elected to the Senate in 2006. Right now, the New York Times has Brown's seat listed as "leaning" toward him for another term, but it's hard to know for sure if that he will keep it.

Angus King is one of a few Independents in Congress. King is a senator representing Maine. He was elected as the state's first Independent senator in 2012, as his Senate website noted. As the aforementioned article from GQ noted, King caucuses with the Democrats and is likely to win another term.

Bob Casey is a Pennsylvania Democrat who was first elected in 2006. Casey is running against Rep. Lou Barletta, a big supporter of President Trump, but the predictions currently "lean" Casey's way, as the Cook Political Report noted.

Deb Fischer is a Republican representing Nebraska. Fischer was first elected to the Senate in 2012, according to her Senate website. There's a pretty good chance that Fischer will keep her seat come November. The Cook Political Report has this race listed as Solid Republican while the New York Times has it as "likely."

Robert Menendez was first appointed to the Senate in 2006, Ballotpedia noted. Menendez is a Democrat who represents New Jersey. As the Washington Post reported, Menendez experienced a corruption scandal, but was ultimately not sentenced to prison. The Cook Political Report has Menendez's seat listed as "leaning" toward him.

Martin Heinrich is New Mexico's junior senator. He was first elected in 2012. He also appeared on Rival Survival, a Discovery Channel show, with Jeff Flake, as Politico reported. Heinrich is running against former presidential candidate Gary Johnson and Republican Mick Rich, as the previously-mentioned article from GQ noted. But it's pretty likely that Heinrich will win another term, as both the Cook Political Report and the New York Times noted.

Ben Cardin is a Democrat from Maryland. He was elected in 2006. The Cook Political Report noted that it's very likely that Cardin will win another term in November.

Sheldon Whitehouse is Rhode Island's junior senator. He's a Democrat who was first elected to represent Rhode Island in 2006. The Cook Political Report noted that chances are good that Whitehouse will win another term.

Tim Kaine is a Democrat representing Virginia and, of course, a former vice presidential nominee. Kaine was first elected to the Senate in 2012. Kaine is very likely to win another term, as the Cook Political Report noted.

Kirsten Gillibrand represents New York as the state's junior senator. Gillibrand is, as the New York Times noted, quite likely to win her race in November.

John Barrasso is a Republican senator representing Wyoming. According to Ballotpedia, he was appointed to the seat in 2007 and won the special election in 2008. He was then re-elected to the Senate in 2012. Barrasso also voted to confirm Kavanaugh. The Cook Political Report noted that Barrasso is very likely to win another term.

Like her fellow Republican senator from Mississippi, Cindy Hyde-Smith also voted in favor of Kavanaugh's nomination to the Supreme Court. Her seat, however, is slightly less safe than Wicker's, according to the Cook Political Report. Still, she is "likely" to be re-elected in November.

Maria Cantwell is a Democrat representing Washington. Cantwell is running against the former head of the state Republican party, Susan Hutchison, but is favored in the race, as the Associated Press reported.

Elizabeth Warren is a Democrat representing Massachusetts. Warren is the senior senator and was first elected in 2012. And as the New York Times noted, Warren is extremely likely to win another term as senator.

Debbie Stabenow was first elected to the Senate in 2000. Stabenow is running against Republican candidate John James, as the Detroit Free Press reported. Stabenow's chance of re-election is currently listed as "likely" by the Cook Political Report.

Tom Carper is a Democrat representing Delaware in the Senate. According to his Senate website, Carper joined the Senate in 2001, leaving his position as governor. The Associate Press reported that Carper is running against the former state Trump campaign chair, Rob Arlett. The Cook Political Report noted that Carper is very likely to win his re-election bid.

You almost certainly know who Bernie Sanders is already, but in case you don't, Sanders is an Independent senator from Vermont. He's the state's junior senator. He's also, of course, a former presidential candidate. He is predicted to win re-election, according to the Cook Political Report.

Though there's still time left before the midterms, they're approaching quickly. Knowing who you might support, whether you'll be voting for a senator or not, is definitely important.