By Moira Warburton and Gram Slattery (Reuters) – Control of the U.S. Senate still had not been determined as of Wednesday afternoon, a day after the Nov. 8 midterm elections. Republicans need to pick up only one seat to take the majority in the 100-seat chamber, which would allow them to block much of Democratic President Joe Biden’s agenda. The chamber is currently split 50-50 between Republicans and Democrats, who maintain control thanks to Vice President Kamala Harris’ tie-breaking vote. Democrats hope to expand their margin. Here are eight races that party strategists are watching closely….