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Wisconsin is very much a target of opportunity for the presidential campaign of Vermont independent U.S. Sen. Bernie Sanders.

With four field offices opened and around two-dozen paid staff expected to arrive before the April 5 presidential primary, the Sanders campaign is "going to go full-court press" to win Wisconsin, state director Robert Dempsey said Sunday.

And the Sanders campaign has a very big local connection.

Dempsey said the campaign is "piggy-backing off the efforts" of the Wisconsin Working Families Party. That liberal group is in the thick of the race for Milwaukee County executive, endorsing state Sen. Chris Larson over incumbent Chris Abele.

"Working Families Party has endorsed Senator Sanders and we want him to win in Wisconsin," said Marina Dimitrijevic, the group's executive director, in a text message.

"We are activating our members to volunteer, knock on doors, and help organize events because we think the more people hear Sanders' compelling message about an economy that works for all of us and not just the wealthy, the more people will respond," she added

Polls have shown a tight primary race here between Sanders and former U.S. Secretary of State Hillary Clinton.

Dempsey headed the Sanders' operation in Minnesota, where Sanders won the caucus. The campaign has done well in parts of the upper Midwest, with a big win in Michigan and a razor-thin loss in Iowa. Clinton easily won in Ohio.

"There is a desire to elect progressive leaders in this state," Dempsey said.

In 2008, Clinton lost the Wisconsin primary to Barack Obama by 17%. This year, she has piled up an impressive list of official endorsements that include U.S. Sen. Tammy Baldwin, U.S. Rep. Gwen Moore and Milwaukee Mayor Tom Barrett.

Dempsey said the Sanders campaign will "end up with an impressive roster of people endorsing."

"We've got a regional strategy," Dempsey said, with more than half of the 86 elected delegates apportioned at the Congressional District level.

The obvious area of strength for the Sanders campaign will be in and around the liberal stronghold of Madison. But with the Working Families Party backing Sanders, it looks there will be a fascinating race within the race in Milwaukee.