The 2022 midterm campaign will barrel to a close eight weeks from now, on Nov. 8. What does history tell us about what to expect? And could 2022 diverge from historical patterns?

Here, we answer those questions.

Historically, what usually happens in midterm elections?

Since at least the mid-1800s, the party that controls the White House has typically lost seats in Congress in the midterm elections.

“The size of the loss correlated, to varying degrees, with the disappointment with the president and the president’s party, the state of the economy, the ebb and flow of turnout for the two parties, as well as occasional scandals or crises,” said Steven S. Smith, a political scientist at Washington University in St. Louis.

Political scientists call this the “thermostatic” effect — voters adjust how they vote, as they would a home thermostat. The common pattern of voters from the opposition party being more energized to vote is closely related; it stems from anger serving as a stronger motivator to vote than contentment.

There have been 19 midterm elections since the end of World War II in 1945. In 17 of those elections, the president’s party has lost seats in the House. The average loss has been 27 House seats. Today, if the GOP gained that many seats, it would be more than enough for the party to become the House majority in January 2023.

Historically, there’s little difference in the scale of House losses during a president’s first midterm versus his second, but the second midterm tends to be worse for Senate races, according to calculations by Charles Franklin, director of the Marquette University Law School Poll.

Usual patterns notwithstanding, there are recent examples of the president’s party gaining House seats, in 1998 and 2002. Those race results have generally been attributed to unusual political moments.

In 1998, the GOP sought to impeach then-President Bill Clinton, an unpopular move among many voters. Clinton’s party gained four House seats that year. In 2002, President George W. Bush rode a wave of early support in the aftermath of the 9/11 terrorist attacks to an eight-seat gain in the House.

Reaching further back, to 1862, adds two additional examples of midterm opposition-party gains in the House. One was 1934, when voters supported President Franklin D. Roosevelt’s plan for combating the Great Depression. The other example was 1902, but that merits an asterisk; the House increased its number of members that year, and both parties gained seats, with the out-party Democrats gaining more.

In the Senate, the historical pattern also tilts toward opposition-party gains, but the tendency is less consistent than in the House.

A president’s party has gained Senate seats in a midterm 14 times since 1862, including six times in the past 60 years: 1962, 1966, 1970, 1982, 2002 and 2018.

The main difference is the Senate’s pattern of staggered elections, in which one-third of the body faces the voters in any given election, rather than every member every two years, as with the House, said John Pitney, a professor of politics at Claremont McKenna College. If the Senate seats contested in a midterm happen to be in states where the president’s party is weak, the party controlling the White House can be especially hard-pressed to gain seats.

A candidate’s individual qualities also matter more in Senate races than in House contests, something Senate Minority Leader Mitch McConnell, R-Ky., has alluded to and that Wayne Steger, a political scientist at DePaul University, echoed.

“The lesser visibility of House races makes it more likely that voters default to their partisan preferences” than in the more widely covered Senate races, he said.

In recent years, the GOP has lost several Senate seats that were considered winnable because the party’s voters nominated candidates who made extreme or controversial comments, said Alan Abramowitz, an Emory University political scientist. Those included Todd Akin in Missouri, Richard Mourdock in Indiana, Sharron Angle in Nevada and Christine O’Donnell in Delaware.

What do the historical patterns suggest about 2022?

In 2022, in both chambers, the Republicans don’t have to win many seats to seize control.

In the House, the Democrats hold a 221-212 edge over the Republicans, with two vacancies. The House’s majority party has only fallen below 222 seats two other times since World War II, when the chamber was without vacancies — the Republicans with 221 from 1953 to 1955 and again from 2001 to 2003.

In the Senate, the Democrats control the 50-50 chamber only because Vice President Kamala Harris can cast tie-breaking votes.

One of the most important predictors of midterm malaise — presidential approval ratings — shows President Joe Biden with weak support nationally. As of Sept. 9, the FiveThirtyEight average of Biden’s approval rating in polls showed him more than 10 points underwater, with 42.5% of voters approving of his performance and 53% disapproving.

Could 2022 break the historical pattern of presidential losses in a midterm?

If presidential approval ratings were all that mattered in predicting midterm election outcomes, Biden’s outlook would be poor. Could 2022 be different? Maybe, ranging from structural factors to news events such as the Supreme Court’s overturning of Roe v. Wade.

With a small House majority, Democrats have fewer vulnerable seats to defend in 2022. Although it’s not uncommon for winning presidential candidates to carry weaker House candidates to victory, Democrats lost 11 seats when Biden won in 2020, including defeats in generally Republican states such as Iowa, Oklahoma, South Carolina and Utah.

Just eight Democrats now represent districts won by President Donald Trump in 2020 (it was seven until Alaska Democrat Mary Peltola won a special election to the House on Aug. 31). By comparison, in 2010, Democrats held 49 seats in districts that had voted Republican for president two years earlier. In that midterm, the Democrats lost 63 seats.

“If the Democrats held 250 seats now, they would be in for bigger losses,” Abramowitz said.

There are fewer truly competitive House seats. Aggressive redistricting and partisan polarization have reduced the number of seats that are considered competitive between the parties.

Decennial redistricting has reduced the number of competitive House seats from 51 in 2020 to about 30 in 2022, out of a total House membership of 435, according to an analysis by David Wasserman of the Cook Political Report.

“This dampens the range of seat swings that are likely,” Smith said.

Meanwhile, increased partisan loyalty in safe districts makes upsets in those districts less likely.

“Split-ticket voting has declined precipitously,” Smith said. “Partisans seem to be breaking from their parties much less frequently, as their antipathy for the other party has intensified.”

Affluent voters tend to vote disproportionately in midterms, and they increasingly vote Democratic. In midterms, voter turnout always drops compared with presidential years. But affluent voters are more likely than other voters to come to the polls in midterm elections.

Historically, this pattern has helped Republicans. But since Donald Trump’s emergence on the political scene, the GOP has increasingly lost affluent voters in the suburbs, while gaining the support of less-affluent voters, notably whites without a college degree. In a midterm, this differential could help Democrats.

This may not be a pure “referendum” election on the president. Usually, midterms are a referendum on the president’s performance. But unlike his predecessors, Trump has kept a high profile since leaving office, seeking to shape the GOP in his image and siphoning away public attention from the current president.

Research by Steger found that between July 1 and Sept. 8, Biden was mentioned in 336 network and cable news stories, but Trump was close behind with 308.

Voters are frequently reminded of Trump and the party he leads: When they hear revelations from the House select committee investigating Jan. 6, 2021; learn more about the FBI’s Aug. 8 search of Mar-a-Lago; listen to his complaints about the 2020 election results; or see him rallying for candidates he endorsed. (He backed 237 candidates in this year’s primaries.)

Trump’s active role in the 2022 midterms could drive core Republican voters to turn out to the polls, but Trump also galvanizes voting by Democrats, even if they’re tepid about Biden.

“Trump’s visibility will remind Democrats why they need to vote,” Steger said.

This could be driving a divergence between Biden’s approval rating and the “generic congressional ballot” — what respondents say when asked by pollsters which party they intend to vote for in Congress. For most of 2022, Democrats trailed Republicans in this metric, but beginning in August, Democrats pulled ahead and were leading on Sept. 9 by just over a percentage point, according to the FiveThirtyEight composite.

Even in a polarized era, candidates still matter. In many cases, Trump has endorsed candidates who are loyal to him and echo his complaints about the 2020 election. This has made these candidates politically controversial and could hurt the GOP’s electoral chances in both chambers.

In the House, Trump-backed candidates could cede seats in the 3rd district of Michigan, the 4th district of Nevada, the 13th district of North Carolina, and the 7th district of Virginia, according to analysis by Wasserman.

In the Senate, Republicans nominated Trump-aligned candidates in evenly divided states such as Arizona, Georgia and Pennsylvania, potentially making it easier for the Democrats to win those races.

Biden may be recovering his mojo at the right time. After a popularity dip that lasted roughly a year, Biden has chalked up some victories in recent months.

Inflation has also shown signs of having peaked, decelerating more than expected in July. And Biden signed several pieces of legislation that demonstrate his ability to work with Congress, including bills to aid computer chip makers; to aid veterans injured by toxic burn pits; and to lower prices for drugs under Medicare, extend Affordable Care Act subsidies and grapple with climate change.

More than anything, the Supreme Court’s decision to overturn Roe v. Wade has energized Democratic voters, especially in states where abortion rights are relatively popular but where new or pre-existing laws could ban the procedure without many exceptions.

“Most people, most of the time, do not pay attention to issues that consume Washington elites,” Pitney said. “Abortion is different. It touches more people more deeply than just about any other issue.”

Experts said that the abortion decision could be at least as much of a motivator as the 1998 impeachment and 2001 terrorist attacks that spurred House gains for the president’s party.

“It’s a game changer,” Steger said. “It has awakened a sleeping giant, with voter registration among women increasing substantially.”

This article was originally published by PolitiFact, which is part of the Poynter Institute. It is republished here with permission. See the sources here and more of their fact checks here.