The consensus among insiders is that Gianforte has a small advantage. Internal Republican polls have been reported to show a race in which Gianforte is up 2 to 4 percentage points. Those internal surveys — while possibly leaked in an attempt to skew the expectations game — do track with assessments from the Cook Political Report and Inside Elections, which give Gianforte only a slight edge.

As always, we’re interested in who wins — a Republican win in Montana gives House Speaker Paul Ryan another member in his majority — but we’re also interested in what the Montana result tells us about the national political environment. And when we’re judging the latter, we need to look at the margin of victory, not just who wins and loses.

Specifically, we’ll want to compare the margin in Montana tonight to previous presidential results in the state. In a neutral political environment, we wouldn’t expect the Montana House special election to be at all close. Montana is about 21 percentage points more Republican than the nation as a whole, according to weighted average of the 2012 and 2016 presidential results.1 (That is, if there were a tie in the national popular vote for president, a Republican would be expected to win Montana by 21 points.)