Wave watch: How the special elections could predict the midterms

Notes: Pennsylvania's Congressional districts were redrawn by the state's supreme court in March 2018. This map reflects the updated boundaries and adjusted PVI. Data: Cook Political Report Partisan Voter Index, Ballotpedia; Map: Chris Canipe/Axios

Democrats have overperformed by an average of nine points in each of the eight special elections since President Trump took office — giving us a sense of what a blue wave might look like in November. This map shows the scenarios for the House races if the Democratic voter turnout resembles the special elections.

Yes, but: Past performance doesn't guarantee future outcomes. A 9-point swing would put the 2018 House race on par with Republican waves in 1994 and 2010, but the generic ballot isn't as favorable. Real Clear Politics had the Democrats up by 13 in December 2017, but by end of this month, their lead was down to 4 points.