Politicians and pundits are scrambling to understand what the recent primary results imply for the upcoming midterm elections on Nov. 6. While reactions have been mixed, many see positive signs for Republicans.

Notable journalists have remarked: “Democrats are divided,” “Republicans, despite being on the defensive, sent a signal of strong support for President Trump,” and “Pennsylvania primary results show surprising Trump strength. Take heart, GOP!”

We think Republicans have much more to be worried about than these comments suggest. A look at 30 years of public opinion data as well as prominent theories of congressional elections suggest that Democrats currently have a major advantage heading into the midterms.

First, Republicans are at a disadvantage because the president’s party tends to lose seats in midterm elections. But this is just the beginning. When presidents are viewed positively their party tends to do better in midterms; when they are viewed negatively, their party does worse.

President Trump’s historically low approval ratings put Republicans at a huge disadvantage. We used data from the Roper Center for Public Opinion Research to show how President Trump’s approval ratings correspond with the past four presidents in April and early May of their second year in office.

President Trump’s average approval rating is about 10 percentage points below President Obama’s ratings during the same period before the Republican landslide of 2010. What should be even more concerning to Republicans is the fact that Trump’s highest rating is below the lowest rating of any of the four previous presidents in April and early May of their second year. Furthermore, President Trump’s approval ratings look similar throughout his entire time in office.

Equally important is the fact that more people report that they “strongly disapprove” of Trump than report they “approve” and “strongly approve” combined.

As a result, Democrats can count on their base being highly energized, leaving them free to focus on local issues or on the unpopular GOP tax cut and effort to repeal ObamaCare. They can follow Conor Lamb’s example – centrist in tone, relatively liberal in substance. His victory in a special election for a Pennsylvania congressional district rested on energized liberals, union members and appeals to moderates.

Tailoring their messages while not dampening liberal energy could help Democrats in Rust Belt districts, suburban districts, and in Republican-held districts carried by Hillary Clinton.

Another indication of the challenges facing Republican candidates comes from a survey questions that asked: “If the elections for Congress were being held today, which party's candidate would you vote for in your Congressional district?”

Relying on data from the Roper Center, we compared the percent who say they would vote Republican during May before each midterm election. The current Democratic advantage (47.3 percent Republican support) is the same as Republicans’ (52.7 percent Republican support) before 2010, when Republicans gained 63 seats in the House.

Considering President Trump’s approval is lower than President Obama’s at the time, Republicans have even more cause for concern. The only midterm election that looked worse for Republicans at this time was in 2006 (43.2 percent), when Democrats gained control of the House and Senate.

Other factors also favor Democrats. The Cook Political Report lists eight Republican-held seats as likely or leaning Democratic, plus 22 toss-ups; no Democratic-held seats are leaning Republican. In special and state elections Democrats have outperformed expectations on average by 13 points.

And then there is the unprecedented number of Republican retirements: incumbents retire when they expect to lose or have diminished influence in Congress (the number Democratic retirements, by contrast, look quite typical).

Still, Democrats are in no position to rest easy. Working against them is the incumbency advantage: it is hard to defeat those already elected into office, although Republican retirements and the large number of qualified candidates Democrats are fielding should help Democrats.

More important is that even if Democrats win a majority of votes they are not guaranteed a majority of seats in Congress. Because districts have been drawn in a way that gives substantial advantages to Republicans, Democrats likely need somewhere between a 7 and 11 percent margin of victory in order to win a majority in the House.

Things are even more challenging in the Senate, which has been called the “most malapportioned legislature in the world.” Only a third of Senate seats are contested each cycle, and the seats up for re-election this year happen to be extremely favorable to Republicans.

What does all this mean? If the election were held today, Democrats would likely win a majority of the votes and make sizeable gains in Congress. Whether this would be enough for Democrats to overcome the disadvantages against them – and take control of the House or Senate – remains to be seen.

Peter K. Enns, is associate professor and executive director of the Roper Center for Public Opinion Research at Cornell University.