It's normal for the party out of power to gain ground in a midterm election. The big question in 2018 is whether the Democrats will gain enough ground to win a majority in the House of Representatives.
While the political winds currently favor the Democrats, 390 of the 435 House races are pretty well locked in for one party or the other. Only 45 out of 435 races are even somewhat competitive. Still, a race-by-race analysis on ScottRasmussen.com suggests that a normal midterm gain would get the Democrats very close to their goal.
The starting point is 187 races that are rated as either Strong or Likely Democratic and nine more tilting or leaning in that direction. With decent midterm turnout, the Democrats would win all of these races bringing their total to 196.
With a good midterm turnout, the Democrats could also win just about all of the toss-ups or races currently just tilting in the GOP direction. These are races like the open seat contest in Washington's 8th Congressional District. Republican incumbent Dave Reichert opted out of a re-election battle in a District where Hillary Clinton attracted more votes than Donald Trump. Barack Obama also carried the District in both 2008 and 2012.
While nothing is certain in politics, Washington-8 is the type of race Democrats should expect to win with a good midterm performance. At ScottRasmussen.com, we place 17 races in this category. Winning all them would get the Democrats to 213 seats, still five votes short of a majority. To get over the top, the current minority party will need an electoral wave that washes out some seats that would remain in GOP hands during a normal election cycle.
At ScottRasmussen.com, we've identified 19 races that currently lean Republican but could be at risk in a wave election. That means the best way to tell if a wave is coming is to follow these 19 races. If the Democrats do well in these campaigns, they will have a very good chance of winning a Congressional majority. On the other hand, if the GOP can solidify its position in these races, there will be no wave and the Republicans will preserve a narrow majority.
The 19 wave watch districts are California-45 (Mimi Walters), Georgia-6 (Karen Handel), Illinois-6 (Peter Roskam), Illinois-12 (Michael Bost), Iowa-1 (Rodney Blum), Iowa-3 (David Young), Kansas-2 (Open), Kansas-3 (Open), Kentucky-6 (Garland Barr), Maine-2 (Bruce Poliquin), Minnesota-3 (Erik Paulsen), Michigan-8 (Mike Bishop), New Jersey-7 (Leonard Lance), New Jersey-11, (Rodney Frelinghuysen), Pennsylvania-7 (Patrick Meehan), Pennsylvania-8 (Brian Fitzpatrick), Pennsylvania-15 (Open) and Utah-4 (Mia Love).
Geographically, many of these districts should be friendly to Democratic challengers. Hillary Clinton won seven of the 19 districts and came very close in five more. Additionally, 10 of the 19 are from states Clinton won in her presidential bid. Four others are from Pennsylvania, a state that the president carried by less than a percentage point in 2016.
Obviously, it's very early in the campaign season and a lot can change by November. But the Democratic path to a Congressional majority must almost certainly pass through these 19 Congressional Districts.