Republican Sen. Pat Roberts leads his Democratic challenger Chad Taylor by only four percentage points, according to a new poll by the independent polling firm Rasmussen Reports.

The poll of 750 likely voters showed Roberts leading Taylor, 44-40 percent, with 8 percent saying they are undecided and 7 percent saying they support someone else.

It was conducted Aug. 6-7, immediately after the primary elections. It reported a margin of error of plus or minus four percentage points.

The poll did not mention independent candidate Greg Orman, who launched a bus tour today to kick off his campaign. As required by law, Orman filed by petition to run as an independent in the general election, but the Secretary of State’s office has not yet received verification of the 10,000-plus petition signatures from county election officers, and so his name does not yet appear on the official list of candidates.

Roberts is seeking his fourth term in the Senate. He survived a primary challenge, winning 48-41 percent over tea party-backed candidate Milton Wolf. But the fact that Roberts failed to win over half the Republican primary vote has given Democrats hope that he could be vulnerable.

“This election is tightening because the people of Kansas recognize that they finally have a moderate alternative in this race,” Taylor said in a statement touting the poll results.

Drilling beyond the overall numbers, the Rasmussen poll showed revealed other interesting trends:

• Roberts does better among male voters (49-38 percent) while Taylor has a slight edge among women (43-39 percent).

• Taylor does better among younger voters (41-32 percent); but Roberts is favored by those age 40 and over.

• Roberts has high unfavorable ratings, while Taylor still struggles with name recognition. Forty-nine percent of those surveyed said they have either a “somewhat” or “very” unfavorable view of Roberts, compared to only 18 percent for Taylor. But 34 percent admitted they had never heard of Taylor.