Last year, amid allegations of sexual misconduct that Kavanaugh denied, the vast majority of Senate Democrats voted against his confirmation.The Senate elections that followed suggest a cautionary tale for Democrats relitigating the Kavanaugh nomination heading into 2020.

Polling models produced by now Washington Post analyst David Byler FiveThirtyEight and I found that the Democrats chance of winning the Senate was slashed from 30%-40% in mid-to-late September (during the Kavanaugh confirmation hearings) to 10%-20% by Election Day. In terms of raw seats, each model had the Democrats winning two to three more seats in late September than they eventually won. Now, some of this may have been natural movement toward the partisan baseline in red states like Missouri and Indiana, but these forecast models are supposed to take into these baselines.

Indeed, the 2018 exit polls suggest that Kavanaugh was a net negative for Democrats across the Senate landscape. One question on some state exit polls asked voters whether a senator's Kavanaugh nomination vote was important to them. In every state but one ( Florida ) where the Republican senator voted for Kavanaugh or the Democratic senator voted against him, it was a net negative for the Democratic Senate nominee.

In these seven states (all but one carried by Trump in 2016), those who said a senator's Kavanaugh vote was important to their choice for Senate were far more likely to vote Republican for Senate. In these states, the Republican Senate candidates won by an average of 18 points among those who said a senator's Kavanaugh vote was important to them. Among those who said the Kavanaugh vote wasn't important, the Democratic Senate candidate won by an average of 7 points.

Perhaps what's most interesting is what the exit polls found in West Virginia , the state where Democratic Sen. Joe Manchin voted for Kavanaugh. Manchin won by 2 points more among those who said his Kavanaugh vote was important to whom they chose for Senate. More stunning, he won by 22 points more among those who said his Kavanaugh vote was any sort of factor (major or minor) in their Senate choice.

In other words, you could make the argument that Manchin's vote for Kavanaugh saved his Senate seat for the Democrats. It's at least a feasible argument that had a few other Democrats such as Indiana Sen. Joe Donnelly voted for Kavanaugh, they might have also held onto their seats too.

Now, what does all of this mean for 2020? To win the presidency, Democrats aren't going to need to win states like Indiana or Missouri. The effect of Kavanaugh nationally is less clear. Kavanaugh had a net negative rating nationally, though the exit polls found those motivated by Kavanaugh were more Republican friendly even in Nevada (where Hillary Clinton won in 2016).

Democrats do need to win red states to take back the Senate. Democrats need a pickup of at least three seats in 2020. Only two Republican held seats up are in states Clinton won in 2016. There's also the one Democratic held seat up for reelection in deeply red Alabama. Put together, Democrats will need to win at least two Senate seats in Trump won states to take back the Senate.

All told, relitigating Kavanaugh may be good politics for a Democratic presidential primary where Kavanaugh is hated. It may even be a wash for Democrats in a presidential general election. It's likely bad politics for Democrats when trying to take back the Senate.