(CNN) - A new survey indicates that Sen. Jon Tester of Montana has his work cut out for him as he fights for re-election.
According to a Mason-Dixon poll conducted for five Montana newspapers, Rep. Denny Rehberg, the Republican challenger, has a 48%-45% edge over the first-term Democratic senator. Rehberg's three-point margin is within the poll's sampling error.
- Follow the Ticker on Twitter: @PoliticalTicker
- Check out the CNN Electoral Map and Calculator and game out your own strategy for November.
Six percent of likely voters say they're undecided, with one percent backing Libertarian candidate Dan Cox.
The poll indicates that Rehberg holds a nine-point 47%-38% advantage among self-identified independent voters. And the survey suggests a gender gap, with Rehberg leading by 14-points among men and Tester ahead by 13-points among women.
Tester narrowly beat incumbent GOP Sen. Conrad Burns by less than 4,000 votes in the 2006 election.
The Mason-Dixon poll was conducted Sept. 17-19, with 625 likely voters questioned by telephone. The survey's sampling error is plus or minus four percentage points.
CNN Political Editor Paul Steinhauser contributed to this report