Tied poll in South Carolina leaves our Senate forecast where it was

A new poll of the South Carolina Senate race shows it even. Impact Research, surveying 800 likely voters between August 18 and 24, put Democrat Annie Andrews at 41 percent and the Republican at 41 percent. It is the only new poll in this race in our payload.

Our forecast did not move. The model gives Andrews a 17 in 100 chance of winning the seat and Republican incumbent Darline Graham an 83 percent chance. Its mean margin is R+11.2, against R+11.3 in the previous run earlier on August 26. The 5th-to-95th percentile range now spans R+29.9 to D+7.9, a shade narrower than the R+30.4 to D+7.5 it showed before. Those are rounding-scale changes, not a reassessment.

The gap between a tied poll and an 11-point projected Republican margin is the model doing what it does: weighing a single survey against the state's underlying partisan lean and the national environment, where our average of 27 generic-ballot polls over the last 45 days stands at D+6.5. One poll at parity moves that blend very little. More polls at parity would move it more.

South Carolina matters to the chamber arithmetic mainly as one of the seats in the Republican column that our simulations rarely reassign. Nationally, our model gives Democrats a 45 percent chance of Senate control and Republicans 55 percent, with a mean of 50.0 Democratic seats. Democrats need 51 seats for control; Republicans need 50, because the vice president is a Republican and a 50-50 tie goes to them. That is the margin on which a race like this one, if it tightened for real, would register.

For now the reading is unchanged: the new number is closer than our projection, and not yet numerous enough to alter it.