The coming midterm elections should be good for Nancy Pelosi and the Democrats in the House of Representatives. However to get control of the chamber they need more than a good year. They need a wave year.

So let’s look at the polls, and see whether a wave looks likely. Remember: the 2016 polls correctly predicted that Hillary Clinton got more votes than Donald Trump.

Let’s first look at the popular vote in the big wave years. In 2010, Republicans beat Democrats 52-45 (R+7) to gain 63 seats. In 2008, Democrats beat Republicans 53-43 (D+10) to gain 21 more seats over 2006. In 2006, Democrats won 52-44 (D+8) to gain 31 seats and control. In 1994, Republicans won 52-45 (R+7) to gain 54 seats and control.

In other years, the results vary. The R+1 2016 resulted in Nancy Pelosi’s side gaining 6 seats, while the D+1 2012 netted the Democrats 8 seats, but not control. The R+1 1998 gained Dick Gephardt 5 seats, but Republicans barely kept control.

So we see what the target for the Democrats is: They likely need to win the national popular vote by at least 7 points in order to take the House of Representatives. As it turns out, that’s exactly where the poll average sits: D+7. Therefore we expect the Democrats, as things stand, to have about a 50/50 shot at taking the House, and making Nancy Pelosi the speaker one more time.

The polls really are right on the line. Some results have the Democrats falling way short (D+2, D+3, D+2), some are borderline (D+6, D+6), and some are over the top (D+8, D+10). Much will depend on whether Republicans and Democrats are motivated to show up next year. Can Trump keep his base excited? Can Democrats find a message to bring their people out?

Next year could be big. Especially since the national election will have coattails into the state elections, which will help determine the post-Census redistricting, a process that greatly benefited Republicans last time around.