The Democrats need to flip 24 seats to win back the House -- here's how they can get there

Democrat Conor Lamb's apparent upset win in Pennsylvania's 18th congressional district is sending shockwaves through the Republican Party, as the district had voted for President Donald Trump by 20 points in 2016.

According to the Cook Partisan Voting Index, PA-18 is rated as a Republican +11 district, which means Republican candidates have a built-in 11-point advantage over Democratic candidates.

What should really concern Republicans, however, is that there are more than 100 Republican-held districts across the country that are rated as less Republican than PA-18 -- meaning dozens of GOP incumbents now find themselves potentially vulnerable.

Based on Cook's Partisan Voting Index, here are the most promising districts for Democratic pick ups.

• Florida 26 (D +6): Currently held by Rep. Carlos Curbelo
• Florida 27 (D +5): Currently held by retiring Rep. Ileana Ros-Lehtinen
• California 21 (D +5): Currently held by Rep. David Valadao
• New York 24 (D +3): Currently held by Rep. John Katko
• Colorado 6 (D +2): Currently held by Rep. Mike Coffman
• Virginia 10 (D+1): Currently held by Rep. Barbara Comstock
• Minnesota 3 (D+1): Currently held by Rep. Erik Paulsen
• Iowa 1 (D +1): Currently held by Rep. Rod Blum
• Washington 8 (EVEN): Currently held by Rep. Dave Reichert
• California 39 (EVEN): Currently held by retiring Rep. Ed Royce
• California 21 (EVEN): Currently held by Rep. Steve Knight
• California 10 (EVEN): Currently held by Rep. Jeff Denham
• Iowa 3 (R +1): Currently held by Rep. David Young
• Texas 23 (R+1): Currently held by Rep. Will Hurd
• Pennsylvania 7 (R +1): Currently held by retiring Rep. Pat Meehan
• New Jersey 2 (R +1): Currently held by retiring Rep. Frank LoBiondo
• California 49 (R+1): Currently held by retiring Rep. Darrell Issa
• Arizona 2 (R +1): Currently held by Rep. Martha McSally, who is vacating the seat to run for Senate
• Pennsylvania 8 (R +2): Currently held by Rep. Brian Fitzpatrick
• Pennsylvania 6 (R +2): Currently held by Rep. Ryan Costello
• New York 19 (R +2): Currently held by Rep. John Faso
• New Jersey 3 (R +2): Currently held by Rep. Tom MacArthur
• Minnesota 2 (R +2): Currently held by Rep. Jason Lewis
• Illinois 6 (R +2): Currently held by Rep. Peter Roskam
• Maine 2 (R +2): Currently held by Rep. Bruce Poliquin

Winning those 25 seats would be more than enough for Democrats to win the majority -- and there are currently seven R +3 seats held by Republicans, as well as 11 R +4 seats held by Republicans. And for the record, House Speaker Paul Ryan's Wisconsin 1 district is rated as R +5, which means even he may not be completely safe from a blue wave.

None of this guarantees Democrats will win all these seats. However, when a Democrat can win in an R +11 district, it shows that the party will have no shortage of potential targets this fall.