Even with the national swift toward the Democrats, Greenfield’s strong standing has been a bit surprising. Incumbent Sen. Joni Ernst, as both a Republican woman and former Army reservist, was a compelling candidate when she ran for the Senate in 2014 and seemed like a rising star in the GOP after she won by 8 points in a state Obama had carried two years earlier. She has probably been more aligned with Trump than a senator from a swing state should be for electoral reasons, but she hasn’t made any major gaffes or had any big scandals in her Senate tenure. And Greenfield, who runs a real estate firm in Des Moines, doesn’t particularly have a unique biography, and she has never been elected to any office before.

Part of the story here is likely that people in politics like me assumed that Ernst was a strong candidate because her 2014 margin looked really big at the time, but that margin was really about Iowa shifting to the right more than Ernst herself. (Trump won big there in 2016.) So Ernst is struggling now because Iowa has moved back left and she doesn’t have much popularity separate from the broader GOP.

Our model has Biden doing slightly worse than Greenfield — or put another way, Trump is doing better than Ernst. That might just be random polling effects, and the presidential and Senate results could end up lining up fairly closely. But there is an obvious explanation for this dynamic: Democrats are spending a lot of money in Iowa to try to win the Senate race, but not much in terms of the presidential race. Biden and various organizations backing his campaign have spent just $3.3 million on TV commercials in Iowa to boost him, according to a recent NPR analysis. That compares with $154.1 million in Florida, the state where they are spending the most. But Democratic-aligned groups have spent more than $56 million in the Ernst-Greenfield race, more than all but one other Senate campaign (North Carolina). This makes sense. Winning a Democratic Senate seat in Iowa is just as valuable as winning one in Texas. But for Biden, Iowa is far less valuable — it has only six electoral votes.