Judging the Kavanaugh effect in key Senate races

There's evidence that in swing states critical to Democrats' Senate hopes in the Midwest, support for Kavanaugh could hurt several incumbent Democrats. Others, less endangered, could see a bump from their opposition to him. The region has become a key battleground in 2018 as Democrats try to regain momentum where Trump beat them in 2016.

Trump's approval rating is at 42% across Midwestern states, according to a recent CNN poll conducted by SSRS, about the same as nationwide, where it's 41%. While the Midwest as a whole didn't support Kavanaugh's nomination to the Supreme Court (40% said to vote in favor, 52% not), many Democratic senators are fighting for re-election in the most deeply red states in the region.

Missouri's senior senator, Democrat Claire McCaskill, is one of those up for re-election. She said the sexual assault allegations against Kavanaugh were "troubling" but were not her reason for voting against his confirmation.

In a Fox news poll released before Kavanaugh was confirmed, 42% of likely voters in the Missouri US Senate election said McCaskill's vote on Kavanaugh wouldn't make a difference in their Senate votes. A quarter said it would make them more likely to vote for McCaskill if she opposed Kavanaugh and slightly more -- 29% -- said it'd make them less likely.

Most people said they had already made up their minds who to vote for -- 75% of likely McCaskill voters said they're certain to support her in November. McCaskill was tied with Republican Josh Hawley at 43% in the poll.

Another Fox poll from the same batch of Midwestern surveys looked at how the Kavanaugh vote might affect the US Senate race in Indiana, where Democratic Sen. Joe Donnelly is hoping to survive a race rated as Toss Up by CNN. For Donnelly, it really is split. A third of likely voters said that if he voted against Kavanaugh's confirmation it wouldn't make a difference how they would vote in the Senate race, 32% said it would make them less likely to vote for him and 30% said it would make them more likely. Donnelly refused to support the judge and voted with his party.

In an NBC/Marist poll in Wisconsin, which is safer Democratic territory that CNN rates as Likely Democratic, a plurality (41%) of registered voters said before Kavanaugh's confirmation that they were more likely to support a congressional candidate who opposed his nomination. In the same poll, Democratic Sen. Tammy Baldwin held a 14-point lead in the race for Senate among likely voters.

Finally, in North Dakota, Sen. Heidi Heitkamp is in dangerous territory. She's a Democrat in a seat CNN rates as Lean Republican and she's been down in the polls. There's evidence that her contentious vote against Kavanaugh might have further hurt her chances. Fox's polling showed 17% of likely voters said her opposition to Kavanaugh would make them more likely to support her, but double that -- 34% -- said it would make them less likely to back her. Nearly half, 46%, said her vote against Kavanaugh wouldn't affect their decision.

Among those who plan to vote for her re-election, 52% said it doesn't make a difference whether she voted to support or oppose Kavanaugh's nomination. However, among those who plan to vote for Republican Rep. Kevin Cramer, her challenger, 54% said her voting against Brett Kavanaugh would make them less likely to vote for her in November.

Trump's approval rating among likely voters in North Dakota in the Fox poll is 64%, significantly higher than the rest of the country and the Midwest as a whole.