History says Democrats are going to gain seats in the House of Representatives in November’s midterm elections, but will they win enough to take control of the chamber?

Midterm elections typically don't go the way of the sitting president. Only three times since 1934 has the president's party gained seats in the House.

Democrats need a net gain of 23 seats. In midterm elections since 1934, the president's party has lost an average of 27 seats, so the law of averages is in the Dems’ favor.

Interactive: House midterm results since 1934

Using data from six political tracking sites, these are the 10 most vulnerable seats for Republicans. Here's a brief look at each of them, in alphabetical order by state, including how the districts voted in the last three presidential elections. This list will be updated regularly as the tracking sites update their forecasts.

Arizona 2nd District

Lea Marquez Peterson (R) vs. Ann Kirkpatrick (D)

2016: Clinton +4.9%; 2012: Romney +1.5%; 2008: McCain: +0.9%

This is the seat Republican Martha McSally is giving up to run for Senate.

California 49th District

Diane Harkey (R) vs. Mike Levin (D)

2016: Clinton +7.5%; 2012: Romney +6.5%; 2008: Obama: +1.0%

Trump endorsed Harkey, while Obama endorsed Levin, pitting the current and former president head-to-head.

Iowa 1st District

Rod Blum (R-Incumbent) vs. Abby Finkenauer (D)

2016: Trump +3.5%; 2012: Obama +13.7%; 2008: Obama: +18.1%

Blum won this district in 2016 by about 8 percent. Finkenauer has Obama’s endorsement. Libertarian Troy Hageman is also in this race.

Kansas 3rd District

Kevin Yoder (R-Incumbent) vs. Sharice Davids (D)

Yet another Trump-Obama endorse matchup. Yoder was first elected in 2010 and has won each election comfortably. A Davids win could make her one of the first Native American women elected to Congress.

New Jersey 2nd District

Seth Grossman (R) vs. Jeff Van Drew (D)

2016: Trump +4.6%; 2012: Obama +8.1%; 2008: Obama: +7.7%

A Libertarian and three independents will also be on the ballot, which could make a difference if the vote is tight.

New Jersey 11th District

Jay Webber (R) vs. Mike Sherrill (D)

2016: Trump +0.9%; 2012: Romney +5.8%; 2008: McCain: +5.1%

Sherrill had reportedly outspent Webber 3-to-1 on this race as of June 30, according to Federal Elections Commission filings.

Pennsylvania

A February ruling by the state supreme court required redrawing of the districts due to Republican gerrymandering. That means some of these districts, as they appear now, didn’t exist a few months ago. The numbers you see for the previous presidential elections, courtesy of Daily Kos, shows how the vote would have gone according to the congressional district lines to be used in the 2018 elections.

Pennsylvania Congressional maps

Pennsylvania 5th District

Pearl Kim (R) vs. Mary Gay Scanlon (D)

2016: Clinton +28.2%; 2012: Obama +27.7%; 2008: Obama +26.5%

This new district is made up of three former districts. The incumbents in two of those are not seeking re-election and the other is running in a different district.

Pennsylvania 6th District

Greg McCauley (R) vs. Chrissy Houlahan (D)

2016: Clinton +9.3%; 2012: Obama +3.2%; 2008: Obama +12.3%

Republican incumbent Ryan Costello decided not to run after the court ruling to redraw this district.

Pennsylvania 7th District

Marty Nothstein (R) vs. Susan Wild (D)

2016: Clinton +1.1%; 2012: Obama +7.0%; 2008: Obama +14.5%

This is another new district made up of parts of three other districts. The original 7th district went to Trump, but it’s believed this new one would have gone to Clinton had it existed in 2016.

Pennsylvania 17th District

Keith Rothfus (R) vs. Conor Lamb (D)

2016: Trump +2.6%; 2012: Romney +4.5%; 2008: McCain +1.9%

The newly redrawn 17th contains pieces of four previous districts. Rothfus currently represents the 12th District and has the endorsement of President Trump. Lamb won the 18th District seat in a special election in March.

INTERACTIVE: 15 more Republican seats in midterm jeopardy

This list was created by compiling and comparing election forecasts from Cook Political Report, Sabato's Crystal Ball, Real Clear Politics, Inside Elections, Fivethirtyeight.com, and CNN. The Republican-held districts listed here were the ones most commonly tagged as “Tilt,” “Lean,” “Likely,” or "Solid/Safe" Democrat, or "toss up."

Information on how previous presidential candidates performed in these districts comes from Daily Kos.

Ballotpedia was also sourced for information on the districts and candidates. Additional information was collected from the Secretary of State offices of individual states.