Sen. Sherrod Brown, D-Ohio, holds a 9-point lead over GOP Treasurer Josh Mandel in the poll. Brown garners 50 percent support to Mandel's 41 percent, with 7 percent of voters undecided. The previous NBC News/Wall Street Journal/Marist poll, conducted earlier in September, showed Brown with a 49 percent to 42 percent lead over Mandel, and the senator has hit or exceeded 50 percent support and held double-digit leads over his challenger in several recent polls.
Meanwhile, Obama leads Romney 51 percent to 43 percent in the survey. The poll was conducted Sept. 30 and Oct. 1 and surveyed 931 likely voters, for a margin of error of plus-or-minus 3.2 percentage points.
In Florida, Democratic Sen. Bill Nelson has a significant lead in his bid for a third term. Nelson leads GOP Rep. Connie Mack, 52 percent to 41 percent. Seven percent of likely voters are undecided on the Senate race. Obama and Romney are in a dead heat in Florida, according to the poll.
Most recent surveys have shown Nelson with a double-digit advantage over Mack. In the previous NBC News/Wall Street Journal/Marist poll, conducted last month, Nelson led Mack, 51 percent to 37 percent. The new Florida poll, conducted Sept. 30 through Oct. 1, surveyed 890 likely voters, for a margin of error of plus-or-minus 3.3 percentage points.