1. While Democrats thought the other three states were in play, they didn't think that was true of Minnesota—so the Russians would have known to target the other three states by virtue of having stolen the Democratic playbook, but not Minnesota.
2. The press hadn't pinpointed Minnesota as being in play in either. For instance, a late October Minnesota Star Tribune poll found Clinton widening her lead to 8 points over Trump. Huffington Post's aggregate found a very similar margin across all polls of the state up to Election Day.
3. There was a lot of Russian troll activity in Minnesota, according to Jamison, who thoroughly researched the topic for her recent book, Cyberwar: How Russian Hackers and Trolls Helped Elect a President. Before release of the Mueller report, Jamison said, "I could never explain why."
4. The Trump campaign clearly thought it was in play and deployed Trump there only two days before Election Day. "With just days left until Election Day, Donald Trump tried to do what 10 Republican presidential candidates have failed to accomplish: Win Minnesota," reported the St. Paul Pioneer Press on November 6, 2016.
Minnesota is the one state that only the Trump campaign thought was in play, that also saw heightened Russian troll activity, and that also made Manafort's exclusive internal poll briefing in August.
"It was unexpectedly close," Jamieson said of the state. "There's my little piece," she added, "that says, Hmm, if there was going to be coordination, on that one I can't explain it from having the Democratic playbook."