From the pollster's analysis:
Manchin still earns high reviews from voters for his job as governor. Seventy percent (70%) approve of his job performance, which includes 36% who Strongly Approve and 34% who Somewhat Approve.
However, there's a gap in support for the governor's Senate run between those who Strongly Approve of his performance and those who Somewhat Approve. While Manchin holds a dominant lead among voters who Strongly Approve of his performance as governor, the race is a virtual tie among those who Somewhat Approve of Manchin's job.
Perhaps one explanation for this divide is that among those voters who Somewhat Approve of Manchin's performance, 64% Strongly Disapprove of President Obama's performance.