Down East 2013 ©
There was only one poll of the U.S. Senate primary races, (from the Maine People's Resource Center, which I had a hand in), so we don't have much of a detailed picture of how voter preferences changed over time in the two races.
Because the survey  was taken at the end of March and beginning of April, however, right after the candidates were confirmed and the campaigns began, a comparison with the actual results on Election Day can give us some idea of what effect the candidates' campaigns had on the results.
Making a direct comparison is difficult, due to the high number of undecideds in April in both races but we can approximate actual voter opinions by assigning the poll's undecided voters based on the choices of those who expressed a preference - basically assuming that undecided voters will either make similar choices to decided voters or won't vote.
Performing this comparison in the Democratic race shows that the last two months of campaigning made almost no difference in voter preference. Almost exactly the same proportion of decided voters supported Dill, Dunlap and Hinck on April 2nd as did at the polls on Tuesday.
This is likely due in part to the lack of a great deal of money in the race and a lack of defining issues or events that moved voter opinions. While Dunlap and Hinck may have had a bit of a monetary advantage, all three candidates were on a similar tier of fundraising and were able to engage in a similar set of campaign activities - mostly direct mail, paid and volunteer phone banks and online advertising. There were no major controversies in the race or ideological differences that received widespread media attention.
The Republican side had a bit more money and a bit more movement, but again initial name recognition and early voter preference predicted the broad outcome of the race.
This race can mostly be characterized by the loss of support for Charlie Summers over time as the other candidates raised their own visibility and as undecided voters made up their minds. In the end, though, Summers still maintained enough of his initial proportion of the vote to win on Election Day.
Money seems to have been a factor in this race, with the candidates who had good fundraising totals appearing to increase their support to some degree. The only two candidates to have a statistically significant increase in support, however, were Scott D'Amboise and Rick Bennett, with Bennett appearing to have run the most effective campaign. In the end it was not enough for him to overcome Summers' and Poliquin's early leads and he remained in third place in the final tally.
The overall lesson here seems to be that the most important factor for this kind of shortened, low-turnout primary campaign is what the candidates have done and how they are viewed before the contests began.
This campaign also proved once again that we shouldn't believe internal polls and claimed metrics of support. Whether it's Poliquin's secret internal poll  or Jon Hinck's unscientific "survey,"  if they don't come with detailed information on results and methods, and sometimes even then, they aren't worth a warm bucket of spit.
Apparently, we also have to be skeptical of candidate's expressed levels of support even after the election.
"State Sen. Cynthia Dill capped a stunning darkhorse run for the Democratic nomination to the U.S. Senate with a convincing win in Tuesday’s statewide primary[...] finishing a stellar campaign which began with few pundits giving her any chance," Dill's campaign declared in a late-night release on Tuesday.
Dill had expressed a very different sentiment a few weeks earlier, in a campaign email:
"The June 12 Democratic Primary is only 27 days away, and thanks to the hard work of our fabulous team and your help, we continue to lead. A Critical Insights poll released last Friday shows that I have the most name recognition among candidates vying for the Democratic nomination. This comes on the heels of an April 6th Maine People’s Resource Center poll that also showed me as the Democratic frontrunner."