Illinois Sen. Mark Kirk trails Democratic opponent Rep. Tammy Duckworth by double digits in a new poll.
Duckworth was supported by 48 percent of likely voters to Kirk's 34 percent in a poll conducted by the Paul Simon Public Policy Institute at Southern Illinois University Carbondale.
Earlier polls have shown Duckworth leading by smaller margins and the Kirk campaign said the last two polls showed the race was closer or a even a dead heat.
"The poll is a clear outlier based on all the other public polling and internal polling we have seen," said Eleni Demertzis, communications director for the Kirk campaign.
Kirk has attempted to brand himself separate from his party in a state that the poll noted hadn't voted for a Republican president since 1988.
The poll surveyed 1,000 registered voters, 865 of them saying they were likely to vote, between Sept. 27 and Oct. 2. It had a margin of error of 3.3 percentage points.
Rothenberg & Gonzales Political Report/Roll Call rates the race Leans Democrat.
In the presidential race, the poll showed Democrat Hillary Clinton leading Republican Donald Trump by a 53 percent to 28 percent margin.