Reports say Democrats will use their new power to investigate Supreme Court Justice Brett Kavanaugh. That could hurt them with voters, just like ruining his reputation did in 2018.

Tuesday wasn’t the blue tsunami many had expected, but Democrats did regain the House while Republicans retained and expanded their majority in the Senate. There are already reports that Democrats are planning to use their newly re-gained power to investigate and impeach Supreme Court Justice Brett Kavanaugh for alleged perjury. However, doing so would overlook the lessons of the 2018 midterms and could hurt them with voters.

Democrats’ Senate position was precarious going into 2018. Democrats were defending 25 of the 33 seats up for reelection. According to Sabato’s Crystal Ball, this was the most overextended a party has been in a midterm in nearly 50 years.

More than that, 10 of Democrats’ 25 seats were in states President Trump won in 2016. Thus, Democrats had an uphill battle going in. However, the controversy over confirming Kavanaugh to the Supreme Court appears to have hurt them further.

Although the president’s party typically loses seats in a midterm and Trump is not a popular president, Republicans gained seats in the Senate. Republicans flipped Democratic seats in Missouri (Claire McCaskill), Indiana (Joe Donnelly), North Dakota (Heidi Heitkamp), and maybe in Florida (Bill Nelson).

As of this writing, Republican Rick Scott leads Democratic incumbent Bill Nelson by less than a percentage point for the Florida Senate race, which will almost surely head to a recount. In Montana, Republican Matt Rosendale took a surprise lead against incumbent Democrat Jon Tester for much of election night, only to be inched out by about 14,000 votes. Each of these are red states that went for Trump in 2016, and each of these Democratic senators voted against confirming Kavanaugh.

Polling had indicated that red-state Democrats McCaskill (MO-D) and Heitkamp (ND-D) might be in trouble. Statisticians at FiveThirtyEight estimated that Heitkamp had a 1 in 4 chance of winning. Despite being the Democratic incumbent during an anticipated “blue wave,” McCaskill was only slightly favored to win, with an estimated 4 in 7 chance. Models predicted these senators were doing worse than other red-state Democrats like Donnelly in Indiana, Tester in Montana, and Joe Manchin in West Virginia.

Why? Some hypothesized that perhaps gender bias was hurting Heitkamp and McCaskill. Some argued that Republican voters are harder on female Democratic candidates because they perceive them as more liberal due to their sex. But election night painted a different picture.

Red-state Democrats who voted against confirming Kavanaugh lost their seats or barely held on, and not just McCaskill and Heitkamp. Manchin was the lone Democrat who voted to confirm—and he handily won without major surprises.

In Indiana, incumbent Democrat Donnelly lost despite the race not even being considered a toss-up by FiveThirtyEight, and their statisticians giving him a 5 in 7 chance of winning. Republican challenger Mike Braun appears to have received a higher share of the vote than statisticians predicted Donnelly, his opponent, would earn.

Another surprise was in Florida, where Democratic incumbent Nelson, who was favored with a 7 in 10 chance of winning, is trailing Republican Scott by 30,000 votes. The race is still too close to call. Tester of Montana nearly lost his race too, barely claiming victory the day after the election, despite strong predictions in his favor and that many perceived his Republican challenger as not authentically Montanan. McCaskill and Heitkamp both lost their seats to their Republican challengers, Josh Hawley and Kevin Cramer, respectively.

The Kavanaugh hearing didn’t just appear to affect sitting Democratic senators, but Democratic hopefuls too. Early on in Tennessee, Democratic Senate candidate Phil Bredesen, a popular former governor, led the polls. In his gubernatorial re-election in 2006, he won all 95 of Tennessee’s 95 counties. Pop star Taylor Swift even entered the political fray to endorse him. However, Republican Marsha Blackburn pulled ahead at the end of September. What happened?

On September 27, Christine Blasey Ford testified before Congress, alleging that Kavanaugh had sexually assaulted her more than 35 years ago when they were teenagers. Many Democrats felt her testimony was sufficient evidence to consider Kavanaugh guilty of the accusations, and refused to confirm him. Hawaii Sen. Maxie Hirono argued that to do otherwise would be to condone sexual assault and tell victims “that they do not deserve justice.”

Many Republicans felt Democrats’ handling of the Kavanaugh allegations were unfair and violated the spirit of due process. Bredesen’s polls never recovered, and Blackburn won with about an 11-point margin.

Exit polling also indicates that the voters who cared about Democrats’ Kavanaugh confirmation vote swung Republican. Among those who said their senator’s Kavanaugh vote was important to them, majorities voted for the Republican challenger:

Indiana: 59 percent voted for Braun (R)

Missouri: 55 percent voted for Hawley (R)

Montana: 68 percent voted for Rosendale (R)

North Dakota: 63 percent voted for Cramer (R)

Those who did not care about the Kavanaugh vote opted for the Democratic incumbent.

Florida was an exception: voters who cared and who did not care about Nelson’ vote were about equally likely to support Scott. These data strongly imply that red-state Democrats’ voting against Kavanaugh doomed their chances in the midterms.

It’s useful to understand why the Kavanaugh vote mattered so much to these Republican voters. First, Democrats and Republicans seemed to view the values at stake differently. Many Democratic voters viewed Democratic senators as protecting a victim and standing up to a sexual predator.

However, many Republican voters viewed Democratic handling of the Kavanaugh confirmation as a violation of basic fairness. They were horrified by the cultural precedent that Democrats appeared to endorse: that an allegation without evidence beyond the memory of one individual person could be enough to destroy a person’s reputation forever.

Many Democrats did not believe these accusations would destroy Kavanaugh’s reputation or life, and some didn’t care if it did, but many who voted Republican thought differently. They did not believe that Kavanaugh was getting his just deserts, but was being punished regardless of the facts. This violated their deeply felt ideas about basic fairness and they reacted by heading to the polls.

Just as one could easily argue that the Democratic takeover of the House was a public referendum on Trump, one can also make the case that the Republican gains in the Senate were a referendum on Democrats’ handling of Kavanaugh’s confirmation. Those seeking to re-open the public debate over Kavanaugh may find that it plays well to an energized base of progressive activists. However, it also mobilizes another base of voters who view the values at stake through an entirely different lens, and this may not help Democratic chances in 2020.