(CNN) - Republicans may be inching closer to a key Senate pickup in the swing state of Colorado.
Republican nominee Ken Buck now leads appointed Democratic incumbent Michael Bennet by 8 points among likely voters, 50 to 42 percent according to a new McClatchy-Marist poll.
Six percent of likely voters remain undecided, while 2 percent are backing someone else.
The race is much tighter among registered voters as a whole, where Bennett is clinging to a statistically insignificant 1-point lead, 41 to 40 percent.
The results are similar to a CNN/TIME/Opinion Research Corporation poll released September 22, which showed Buck leading Bennett by 5 points, 49 to 44 percent among likely voters. Bennett held a 47 to 44 percent lead among registered voters in the CNN/TIME/ORC poll.
Buck, the Weld County district attorney, was once a long shot in the battle for the GOP nomination. But thanks in part to support from some in the Tea Party movement, he defeated former Lt. Gov Jane Norton, who was recruited to run by national Republicans and was the early favorite in the race.
Bennet survived a spirited Democratic primary challenge from former Colorado House Speaker Andrew Romanoff. He was appointed early last year to replace Democratic Sen. Ken Salazar, who stepped down to serve as Interior Secretary in the Obama Administration.
The McClatchy-Marist poll was conducted September 26-28 with 822 registered voters in Colorado, including 537 likely voters questioned by telephone. The survey's sampling error is plus or minus 4.5 percentage points for registered voters and 3.5 percentage points for likely voters.