The TV networks NBC and ABC both projected a Republican majority in the 435-seat chamber, which the party has controlled since 2010.
That is because the vice-president is automatically a member of the Senate. They need to gain 4 seats if Hillary Clinton wins the presidency and 5 if Donald Trump wins.
During a TV debate last month Mr Kirk mocked Ms Duckworth’s Thai heritage, but later apologised. The Democrats have so far gained just one seat, with Tammy Duckworth, taking Mark Kirk’s place in Illinois.
Wisconsin Senator Ron Johnson held off Russ Feingold despite widespread expectations of a win for the Democrat. North Carolina was held by Republican Richard Burr. Todd Young saw off a challenge from former Senator Evan Bayh in Indiana. However Republicans hung on to other key seats in Wisconsin, North Carolina, Indiana and Florida.
Republican Senator John McCain won his sixth term at the age of 80 and suggested it could be his last one. In Florida, former contender for the Republican presidential nomination Marco Rubio won re-election.
The 2008 Republican presidential nominee said, “I’m not sure how many more I have in me.” House Speaker Paul Ryan, also won re-election to the House of Representatives in Wisconsin.