At least six U.S. Senate races in toss-up states hang in the balance and could determine who ends up controlling the upper chamber of Congress starting in 2017. Will Republicans maintain control of the U.S. Senate this election year?

Republicans currently hold 54 seats in the Senate and Democrats hold 44; two other senators are independent and caucus with the Democrats. Of the 34 Senate seats up for grabs this election year, 24 of them are held by Republicans. To control the Senate, one party must have a majority of at least 51 seats; since the vice president can break ties, technically that majority can be had by whichever party controls the White House.

That’s why Republicans and Democrats seem to be focusing their efforts in states like New Hampshire, Nevada, North Carolina, Wisconsin, Illinois and Pennsylvania where candidates are running tight races, according to Real Clear Politics, which tracks polls in every race. Senate races in seven other states are also considered highly contested, according to a Roll Call analysis.

Here are some of those races that could determine who ends up controlling the U.S. Senate in the near future.

New Hampshire: Sen. Kelly Ayotte (R) and Gov. Maggie Hassan (D)

As the incumbent, Sen. Kelly Ayotte is running a tight race against Gov. Maggie Hassan in a state where Donald Trump has fallen behind in the polls. Sen. Ayotte maintains a two-point average lead in the polls ahead of Gov. Hassan (with a +2.3 margin of error), according to a Real Clear Politics average from polls this week. Other polls put Gov. Hassan ahead of Sen. Ayotte.

A 2005 tape in which Trump was heard making lewd remarks about women has prompted some Republicans, including Sen. Ayotte, to distance themselves from the candidate. At a debate on AM radio Friday, Ayotte said she would not vote for Trump or Democratic presidential candidate Hillary Clinton and instead would vote for Indiana Gov. Mike Pence as a write-in candidate.

https://twitter.com/NECN/status/783078689215053824

North Carolina: Sen. Richard Burr (R) and Deborah Ross (D)

Democratic challenger Deborah Ross is running neck-and-neck with incumbent Republican Sen. Richard Burr, making North Carolina one of the toss-up states in this election. Sen. Burr has an average 1.9-point lead ahead of Ross, according to polls this week. Trump’s support has also waned here, allowing Clinton to now lead by a few points in most polls.

Unlike Sen. Ayotte, the biggest challenge to Burr has been the statewide discontent with Republicans following the passage of a controversial bill that required transgender individuals to use bathrooms belonging to their birth sex. Sen. Burr has raised almost $9 million in this race alone, which dwarfs Ross’ $4 million raised, according to Open Secrets, an independent website that tracks election money.

https://twitter.com/WFAE/status/786959268406788096

Wisconsin: Sen. Ron Johnson (R) and Russ Feingold (D)

As a Democratic-leaning state where Clinton leads in the polls by an average of seven points, according to most polls, the odds seem to look good for Russ Feingold who is challenging Republican Sen. Ron Johnson. By look good, we mean that he leads in the polls by about 3 points.

https://twitter.com/WPR/status/786987587064004608

Illinois: Sen. Mark Kirk (R) and Tammy Duckworth (D)

The Chicago Tribune recently endorsed Democratic challenger Tammy Duckworth, who leads in the polls by an average of seven points ahead of Sen. Mark Kirk. The campaign, like many, is heating up. Sen. Kirk’s campaign has accused Duckworth of ignoring claims of corruption and mistreatment of veterans during her time as head of the Illinois Department of Veterans Affairs.

Sen. Kirk distanced himself from Trump early in the race when the presidential candidate attacked a Hispanic judge this summer. But the senator has since come under fire for saying President Obama acted “like a drug dealer in chief” for a $400 million cash payment made to Iran.

https://twitter.com/wttw/status/783295611382530048

Pennsylvania: Sen. Pat Toomey (R) and Katie McGinty (D)

Republican Sen. Pat Toomey and his Democratic challenger are neck-and-neck in the polls in a state that’s considered to be a toss up in the election. Even with Clinton leading in most polls, Republicans see Pennsylvania as a key state in order for Trump to gain the edge over his Democratic opponent.

Like many other Republicans, Sen. Toomey distanced himself from Trump’s remarks in the 2005 tape but declined to say whether he would vote for Trump or not. Sen. Toomey’s campaign has a lot more money at his disposal. The senator has raised more than $22 million compared to McGinty’s $6.7 million, according to the Center for Responsive Politics’ Open Secrets database. So far, this is the most expensive Senate race this election.

https://twitter.com/witfnews/status/787020346176204800

Missouri: Sen. Roy Blunt (R) and Jason Kander (D)

Missouri Secretary of State Jason Kander has been a surprise for Democrats in a red state where incumbent Republican Sen. Roy Blunt has kept the lead in the polls. Now, Democrats think Kander has a chance.

The young Democratic challenger, whose military background appeals to conservative voters, recently ran what’s been called one of the best television ads of the election cycle in which he assembles an AR-15 weapon while blindfolded. Some Republicans in the state still think Sen. Blunt is likely to win.

https://twitter.com/stltoday/status/782081008061472768

Come Nov. 8, these are some of the Senate races to keep an eye on.

Will Republicans maintain control of the Senate? We’ll keep you posted if and when that happens.

Email: luis.gomez@sduniontribune.com

Twitter: @RunGomez