To what extent did the Panama Papers affect the outcome of the Wisconsin Democratic Primary?

Question

A few weeks before the primary, polls showed Clinton was favored to win the Wisconsin Democratic primary. Then the Panama Papers were leaked, in many ways validating and reinforcing Sanders' campaign themes, and Sanders ended up winning the Wisconsin primary by 13-14 points. Although I've noticed that polling in a lot of states have swung heavily toward Sanders in the last few weeks before their primary or caucus. Can any of that be attributed to the leak, and how much is it likely to affect future primary contests like New York?

Answer 1

The Panama Papers were released on April 3rd. Sanders already had a lead in Wisconsin according to polls taken before April 3rd and the release of those papers.

According to an Emerson college poll conducted during the time period of March 30-April 3 had Sanders leading by 8 points ahead of Clinton.¹ Various other polls conducted during the close of March and beginning of April had Sanders in the lead, or Clinton up by 1-2 points (with the exception of one 6 point lead, also from Emerson college, according to a list compiled by FiveThirtyEight.

Sanders "comeback" in Wisconsin can be attributed to the lack of polling done in the state. Between November 16, 2015 and March 20th, 2016, the aforementioned list from FiveThirtyEight notes only two polls in the state. With Clinton being an effectively uncontested front-runner until January of this year, that leaves a significant gap in polling to gauge interest in the state as Sanders's campaign took off in earnest.

As for his recent successes (which, to your question, were much before the Panama Papers release), much of that can be attributed to Sanders's popularity in smaller states, as well as the lack of Clinton's key demographics in the six most recent Democrat contests (notably minority voters and the elderly). Being on a run of victories is also helping propel the Sanders campaign in recent weeks, and Sanders has become a bit more mainstream which helps voter relate to him (even if it is as simple as "I saw Larry David pretend to be that guy on SNL!").