A surprise brewing in South Dakota's Senate race?

Late in the game, it's looking like a three-way race in South Dakota, with Independent Larry Pressler pulling support from Republican Mike Rounds. Once viewed as a spoiler, Pressler may be on his way to becoming a contender.

For months now, the Senate race in South Dakota, which is open due to the fact that Sen. Tim Johnson (D) is retiring, has been seen as an easy Republican pickup. Former Gov. Mike Rounds easily won the GOP nomination for the seat has been, and continues to be, the frontrunner in the race. One potential curve ball in the race has been the Independent candidacy of former Sen. Larry Pressler, who represented the state from 1979 through 1997 as both a congressman (back in the day when South Dakoka still had two Congressional Districts) and later as senator, who entered the race late last year in what many viewed at the time as a quixotic bid for a comeback. As it turns out, Pressler has polled stronger than many had expected, no doubt in some part due to name recognition, but a new poll is raising questions about whether he could pose a threat to Rounds in November:

Independent Larry Pressler continues to steal support from Republican Mike Rounds in the race for US Senate, while Democrat Rick Weiland falls behind, a new poll shows.

Survey South Dakota – conducted by Survey USA on behalf of the American News, KSFY TV of Sioux Falls and KOTA TV of Rapid City – was of 616 likely voters and was conducted between Oct. 1 and Sunday. It shows 35 percent of those responding will vote for Rounds, 32 percent for Pressler and 28 percent for Democrat Rick Weiland. Three percent of voters back independent Gordon Howie and 2 percent are undecided, according to the poll. It has a margin of error of 4 percent.

A Survey USA poll released a month ago showed Rounds with 39 percent support, Weiland with 28 percent and Pressler with 25 percent.

Were Weiland to drop out of the race, 71 percent of his voters say they would back Pressler compared to only 9 percent for Rounds. That would give Pressler 54 percent of the vote compared to 39 percent for Rounds. As things stand, though, Rounds could be elected with less then 40 percent of the vote, the poll shows.

Should Pressler drop out, the race would be a dead heat between Rounds and Weiland, with each major party candidate picking up 47 percent of the vote, according to poll results.

With all three men on the ballot, Rounds is backed by only 55 percent of Republican Party base, according to the survey.

(…)

Among voters 50 to 64 years old, Pressler is the most popular candidate in the Senate race. Among those surveyed who are older than 65, Rounds is the top choice, according to the poll. It also shows that the economy is the most important issue in South Dakota congressional races, with health care a distant second. The economy is the most important issue to Republicans, Democrats and independents, according to the survey.

There hasn’t been a whole lot of polling in South Dakota this year, but what there has been has shown Rounds in the lead in what has turned into a three-way race, thanks to Pressler’s stronger than initially expected showing in the polls. Polling conducted prior to the release of this poll showed Rounds up by 15 points and 13 points, respectively, and even with this new poll added in, Rounds maintains an 11.7 point lead in the RealClearPolitics average. As with the poll we saw earlier this week from Kentucky, though, this new poll raises the question of whether we’re looking at an outlier or the indication that the race is changing in the final month thanks largely to a rise in support for Pressler, who had been a fixture in South Dakota politics until being defeated in 1996 by the senator whom he now seeks to succeed. Up until now, Pressler has seemingly played the role of spoiler by preventing either candidate from getting anywhere close to 50% of the vote in a poll, but the question now is whether he’s likely to become a real contender.

As with the poll that purports to show Alison Lundergan Grimes leading in Kentucky, it is best to take this single result with a grain of salt. As with Kentucky, all of the polling to date has shown Rounds, and indeed with a very strong lead, so a single poll that shows something different should be viewed suspiciously until there are others polls out there that seem to corroborate it. Additionally, it’s worth noting that, like Kentucky, this is a SurveyUSA poll and it was released on the same day as a SurveyUSA poll of the Kansas Senate race that showed Greg Orman with a smaller lead over Pat Roberts than any of the other recent polling. While its possible that SurveyUSA is picking up something that other pollsters are not, it’s also possible that these three polls are indicative of something quirky in their methodology that is causing them to come up with results that are outside of the mainstream. Again, we’ll have to wait to see what other pollsters have to say.

Nate Silver comments on the new poll and what it might mean for the race:

This is a challenging race to forecast – both because of the inconsistent polling and the three-way dynamic. But the logic programmed into the FiveThirtyEight model is as follows: because Pressler is more ideologically similar to Rounds than Weiland  at least according to the statistical measures that we use — the model assumes that Pressler and Rounds will mostly trade votes with one another rather than with Weiland. In other words, Pressler’s gains will tend to come at Rounds’ expense, and vice versa. (See here for a more technical explanation.)

That makes Pressler the more likely candidate to pull off the upset; he can gain ground relative to the frontrunner more quickly. The FiveThirtyEight model currently gives Pressler a 9 percent chance of winning the race, versus 3 percent for Weiland. Those chances will grow if more polls come along with results like SurveyUSA’s.

Yet another complication is that Pressler has refused to say who he’ll caucus with. Our ideology ratings imply that he’s equivalent to a moderate Republican – just as they imply that Orman is equivalent to a moderate Democrat. So the model assumes there’s a 75 percent chance Pressler would caucus with Republicans if he wins, just as it assumes there’s a 75 percent chance Orman would caucus with Democrats. But Pressler endorsed Barack Obama in both 2008 and 2012 and has at times implied that he’d refuse to caucus with anybody.

Rounds remains the favorite. It’s not clear that Pressler has enough money to run a substantial number of advertisements in the closing days of the campaign – or to finance a voter turnout operation. And for the time being, the SurveyUSA poll is mostly alone.

But the race increases the chance that we’ll have a “messy” outcome on Election Day.

So, stay tuned on this one, but suffice it to say that if the GOP has to start worrying about South Dakota this late in the game, its going to play havoc with their game plan for the last month of the race.

Doug Mataconis appears on the Outside the Beltway blog at http://www.outsidethebeltway.com/.