Most political stories covering the 2018 House of Representatives campaigns commonly promote the impression that the Democrats are a virtual lock to usurp the Republican majority. But, a closer look at the numbers and facts suggests a much different outcome.

Much has been made about a new president’s party failing in the midterm directly after his initial national election, and this justifies many partisan claims that Democrats will do very well come the 2018 vote. Looking at the modern political era (post-President Harry Truman, inclusive), the average loss for the new president’s party is 26 House seats in first midterm, while the Senate average is only two. But simply finding the mean doesn’t tell the entire story.

Democrats need a net gain of 24 House seats to obtain a one-seat majority. Because they must defend 25 of the 33 in-cycle Senate states, Republicans are a virtual lock to retain the majority in that legislative body. The Democrats have only two viable Senate targets (Nevada and Arizona), and they need a net of three to claim majority status. And, they must defend 10 senators in states that Donald Trump carried, nine of which elect a Republican to the state’s companion seat. Since the Senate majority is not in play, the House becomes the Democrats’ key 2018 political playing field.

Since Truman assumed office in 1945 and stood for election in his own right in 1948, 11 presidents have seen his party lose House seats in the first midterm election. President Gerald Ford, because he was never elected to the office, is not included for purposes of this statistical exercise.

While true that the average result in these elections is a minus 26 seats for the president’s party, the six Democratic presidents — Truman, John Kennedy, Lyndon Johnson, Jimmy Carter, Bill Clinton and Barack Obama — have averaged a 35 seat loss, while the average GOP downturn for its five post-World War II elected presidents — Dwight Eisenhower, Richard Nixon, Ronald Reagan, George H.W. Bush and George W. Bush — is only 15 seats.

The averages are skewed because three Democratic presidents — Johnson, Clinton and Obama — saw massive losses during their first midterm. Democrats under Johnson lost 47 House seats in 1966, while 54 were dropped under Clinton in 1994, and 64 when Obama had been the nation’s chief executive for two years in 2010. These numbers contrast greatly when compared to the three Republican presidents losing the most seats in their first midterms: Reagan, 26; Eisenhower, 19; and Nixon, 12.

While all presidents’ political parties have absorbed House seat losses during the first midterm vote after a president’s initial election, the same is not true for Senate elections. In fact, in four presidents’ first midterm (Kennedy, Nixon, Reagan and George W. Bush), the “in party” actually added Senate seats. Presidents Kennedy and Reagan saw two-seat Senate gains, while Nixon and Bush each found Republicans adding one.

Another factor is redistricting. In three of the aforementioned presidencies, the first midterm was also a redistricting election year. Thus, the loss totals are skewed depending upon which party held the redistricting pen.

The three presidents elected in the new census “zero year” are the ones affected here: Kennedy (1960), Reagan (1980), and G.W. Bush (2000). In their first midterms, Kennedy and Bush had an edge because their own political party held the redistricting advantage, thus controlling the pen in most states. As noted, Reagan experienced the highest loss of any Republican chief executive, but his is the only instance where redistricting was dominated by the opposing party.

Therefore, the large 26-seat Republican loss in the first Reagan midterm was, to a considerable degree, explained by an unfavorable GOP redistricting outcome in most of the affected states.

The 2018 Democrats also have two other factors cutting against them. Reversing the trends in the most recent elections, the present election cycle looks to feature a low number of open seats. Since incumbent retention ratios are always extremely high in House elections, a large number of open seats generally helps the minority party make up political ground. So far, we only see 15 regular election open seats, and Democrats must protect six of those. In only one instance, that of retiring Rep. Ileana Ros-Lehtinen’s south Florida district, is an open Republican seat even in the toss-up column.

Another obstacle for Democrats to overcome is the relatively few number of highly competitive seats that currently appear on the horizon. Of the nine toss-up districts that can be reasonably categorized as such, Democrats must protect four. Of the eight members who won with less than 50 percent pluralities last November, thus signaling a high degree of vulnerability, four are Democrats.

Going in their favor, however, could be redistricting lawsuits in Pennsylvania and Texas. If the courts force partial redraws in those states before the 2018 elections, Democrats could benefit with many more Republican seats becoming competitive.

Moving into 2018, the first midterm election under Republican President Donald Trump, these deeper historical statistics in and of themselves do not necessarily predict Republicans will lose enough House seats to swing control to the Democrats.

Looking at the loss factor within a partisan context, and taking into account the current low number of open competitive districts where Democrats have an offensive opportunity, it is becoming clear that the minority party must substantially exceed the average historical performance if they are to create the new majority many in the media are already predicting.