By Kyle Trygstad

South Dakota Rep. Stephanie Herseth Sandlin has a race on her hands. A new poll shows the Blue Dog leader down 12 points to state Rep. Kristi Noem, who defeated two legitimate opponents to win the Republican nomination Tuesday.

Noem leads 53 percent to 41 percent in today's Rasmussen poll. Previous polls by Rasmussen showed Noem down 15 points in April and 3 points in May.

The result may reflect a bounce in the polls that many primary winners receive shortly after their victories. But Herseth Sandlin, running for a fourth full term, clearly could be in trouble polling in the low 40s at this point in the election year.

Herseth Sandlin has won re-election with nearly 70 percent in her last two elections. She was first elected to Congress in a 2004 special with 51 percent, then elected to a full term later that year with 53 percent.

This year, a quarter of the state's voters consider themselves part of the Tea Party movement, according to this latest poll, and Noem has the support of more than 80 percent of them. And President Obama, who took 45 percent of the vote in the state, now has an approval rating there of 40 percent.