West Virginia Gov. Joe Manchin (D) was supposed to have an easy road to the Senate once Rep. Shelley Moore Capito (R) decided against challenging him in November's special election.

But the latest Rasmussen poll on the race shows Republican businessman John Raese within six points of the popular governor.

Manchin is running in a special election to fill out the remainder of the late Sen. Robert Byrd's (D) term.

The new poll gives Manchin 48 percent of the vote to Raese's 42. Another 4 percent prefer another candidate, and 7 percent remain undecided. The survey polled 500 likely voters and has a margin of error of plus-or-minus 4.5 percentage points.

An earlier Rasmussen poll on the special election had Manchin up 51-35.

Even though he holds just a six-point edge, Manchin's overall approval is high. The poll found that 70 percent of likely voters approve of the job Manchin is doing as governor.

So what's dragging Manchin down? Rasmussen suggests it's President Obama's unpopularity in the state, which Manchin's Republican opponent has made the hallmark of his campaign. Raese, who is expected to pour plenty of his own money into the campaign, has already run TV ads hitting the president.

Among the 34 percent of voters who just "somewhat approve" of the job Manchin is doing as governor, 64 percent strongly disapprove of the president's performance. Raese also holds a 45-40 edge among unaffiliated voters in the state.

The Raese campaign quickly trumpeted the results of the poll in an e-mail blast, while Manchin's camp dismissed Rasmussen as a "Republican pollster."