Idaho poll leaves Risch far ahead, and our margin drifts wider

A Change Research survey of 1,213 likely voters in Idaho, fielded July 28-30, put Republican Sen. Jim Risch at 43 percent, independent Todd Achilles at 19 percent and an unnamed Democrat at 13 percent. Roughly a quarter of respondents fell outside those three options.

The poll did not change our assessment of who wins. Our model gives Risch a 100 percent chance and Achilles a 0 in 100 chance. It did move the expected margin slightly: our mean is now R+19.2, up from R+18.6 in the previous run on Aug. 20. Our 5th-to-95th percentile range runs from R+30.4 to R+8.2, a wider band than the point estimate suggests, and one that reflects how little of the Idaho electorate the available polling has pinned down.

That is a reversal in direction from the small narrowing we reported a day earlier, and it is a reversal of the same size — under a point of margin, with the win probability untouched at either end. In a race our model treats as settled, movement of that scale is bookkeeping rather than news.

The national picture is where the uncertainty sits. Our model gives Democrats a 48 percent chance of Senate control and Republicans 52 percent, with a mean of 50.2 Democratic seats. Democrats need 51 seats and Republicans need 50, because the vice president is a Republican and a 50-50 tie goes to the Republicans. Our generic-ballot average stands at D+6.7 across 24 polls in the last 45 days. Idaho is not one of the seats that decides which side of that line the chamber lands on.