The common belief is that the Independence Party candidate for governor siphoned votes away from the DFL candidates in 2002 and 2006, but this year, Republicans, along with groups that generally align themselves with the GOP, might have reason to worry.
That's because the IP's endorsed candidate is a former Republican who believes he can draw moderate Republican support away from the GOP's endorsed candidate, Rep. Tom Emmer. Some Republican-leaning groups are taking Horner very seriously.
"He is one of the candidates that we would look upon a viable candidate, and a real threat to the progress that we made under the last eight years with Gov. [Tim] Pawlenty," said Scott Fischbach, executive director of Minnesota Citizens Concerned for Life, a group that lobbies against legalized abortion.
MCCL has issued several press releases and posted several entries on its blog criticizing Horner. Fischbach says Emmer is the only candidate in the race who is not, in his words, "pro-abortion."
"There's a clear, clear distinction between these five leading candidates right now for governor," Fischbach said. "There is only one who will stand up for life. The other four will not."
But the MCCL has said little about the Democrats in the race. Fischbach said that's because they already have clear voting records, and Horner doesn't.
It isn't odd for MCCL to attack a candidate that disagrees with its views, but it's unusual for the group to focus this much time and effort on Horner this early in the campaign.
MCCL isn't the only one. A group called the National Organization for Marriage is running a statewide television ad that singles out Horner and the three DFL candidates for governor.
The Minnesota Family Council's Chuck Darrell, who is speaking for the group that's running the ad, said his organization can't endorse candidates. But, he said, Emmer is the only one who supports a constitutional amendment that defines marriage as between one man and one woman. Darrell said it remains to be seen if Horner will eat into Emmer's Republican base of support.
"I think a lot of people are looking for a true conservative. That would be a conservative who is not only conservative on social, financial, government, jobs and economic issues but also one who is conservative on social issues like marriage as well," Darrell said.
Horner said he isn't surprised by the criticism. He said the Republican Party and GOP-leaning groups are criticizing him because they're worried about Emmer's stance on issues like the budget and health care.
"I think they see in me that there are many Minnesota Republicans, the Dave Durenberger, the Arne Carlson and the Jim Ramstad kind of Republicans who are not going to move over to a Tom Emmer," Horner said.
"I think Tom Emmer is so far out of the mainstream that that has those narrow interest groups very concerned. So they need to tear me down because they have a weak candidate."
Horner does support allowing same-sex couples to marry. He also said said he's committed to reducing the number of abortions in the state, but has criticized a law requiring a 24-hour waiting period before a woman can have an abortion. He said he would not push to end public funding for abortions. Both are top MCCL initiatives.
Carleton College professor Steven Schier said groups are trying to solidify conservative support for Emmer. He said he thinks some moderate Republicans may see Emmer as too conservative.
"Tom Horner is a threat because he has a Republican background and may well crack the Republican base and take significant Republican votes away from Tom Emmer and deny the governorship to Tom Emmer," Schier said.
Schier said he expects conservative and liberal interest groups to ramp up attacks on Horner if polling shows he's picking up support.