Tommy Thompson holding narrow lead in Wisc. GOP Senate primary

Tommy Thompson, the former Wisconsin governor and U.S. health secretary, holds a narrowing lead in the bitter Dairy State Republican U.S. Senate primary with less than a week to go before the Aug. 14 vote, according to a new poll from the Marquette University Law School.

The survey, however, showed that more than 1 in 5 likely primary voters were still undecided, giving a measure of hope to Thompson’s three rivals, including deep-pocketed hedge fund investor Eric Hovde whom the former governor led by 28% to 20% in the survey.

Former U.S. Rep. Mark Neumann was backed by 18% of those surveyed while Wisconsin Assembly Speaker Jeff Fitzgerald, a close ally of current Gov. Scott Walker, had the support of 13%.

Marquette polls in June and July showed Thompson holding much larger leads in the contest.

A flurry of polls in recent days had the contest slipping into a statistical dead heat between Thompson, Hovde and Neumann, and Hovde was quick to question the validity of the Marquette survey, dismissing it as an “outlier.”

However, the Marquette survey proved highly accurate in predicting the outcome of last June’s recall election for governor, which Walker won by 7 points over Democratic challenger Tom Barrett.

Charles Franklin, the Marquette poll director, said one difference between his survey and others is that it takes into account cellphone numbers while the others do not. Americans in increasing numbers are dropping land lines and using cellphones as their primary communication technology, creating new challenges for pollsters.

The winner of the GOP primary will face U.S. Rep. Tammy Baldwin of Madison who has no Democratic primary opposition. No matter which Republican wins on Tuesday, the survey showed the Senate contest with Baldwin at this stage was tight.

In a theoretical Thompson-Baldwin match, the former governor was the choice of 48% of voters surveyed statewide while the Democrat was favored by 43%. In a Neumann-Baldwin face-off, each gets 44%, while Baldwin tops Hovde 44% to 41% and Fitzgerald by 45% to 40%.

All four matchups were within the poll’s margin of error, which was plus or minus 2.9 percent. The survey of general election sentiment, which involved 1,188 likely Wisconsin voters, also showed that President Obama held a 5 percentage point advantage over Republican Mitt Romney in Wisconsin, slightly smaller than Obama’s edge in a Marquette poll last month.

Follow Politics Now on Twitter

bsecter@tribune.com