If this election year ushers in as big a wave as Democrats are hoping for, it could end not just with a new party in control of the House, but with a major brain drain in the chamber. Departing members take with them their institutional knowledge and experienced staff. The freshmen who replace them will not only be starting from scratch, but, like Tea Party members did in 2010, could arrive by virtue of an antagonistic attitude and may be reluctant to back established party leadership.

The 69 representatives who for one reason or another won’t be a part of the House membership next year represent a significant portion of the House’s cumulative experience, a combined 828 years of experience in the chamber — roughly a fifth of the House’s total at the time this Congress began. 

Already, an unusually high number of House members have announced their retirements. The 31 so far include some of the most senior members of Congress, namely Reps. Sander M. Levin — a Michigan Democrat in his 18th term — and Republican Joe L. Barton of Texas, who is in his 17th. The House’s highest ranking member and 10-term veteran, Speaker Paul D. Ryan of Wisconsin, has also said he is not running for re-election.

In addition, 14 members have resigned or have indicated they plan to resign before the session is over. Chief among them was Rep. John Conyers Jr., who was accused last year of sexual misconduct while in office. He was first elected as a Michigan representative in 1964, and was, at the time of his resignation, the sitting member with the most House service.

Another 21 House members have said they are going to run for a different political office and give up their seats.

Louise Slaughter, a New York Democrat who served for 30 years, died in March, and Republican Rep. Robert Pittenger of North Carolina lost his party’s primary Tuesday.

These departures will result in a less experienced House for the 116th Congress, and if they are coupled with a wave of defeats in the November elections, it could leave the chamber at a level of inexperience not seen since the 1990s, according to a Roll Call analysis of tenure and election data.

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How this could happen

When more incumbents lose their seats and are replaced by freshmen, the average experience of the chamber goes down. But this effect is somewhat offset by the increase in experience among members who are re-elected.

How much does the average experience go down when members lose? It works out to a little more than one week per defeated member, on average. So if 52 members lose, the average House member’s experience generally sinks about one year lower than it was before the elections, after accounting for retirements.

But what does that mean for the House in the 116th? Here are three instances to think about, where we use those averages to make some predictions about what would happen to the experience level under certain scenarios:

1. We see a wave election à la 2010: 58 losses

The similarities between 2018 and 2010 have been hashed out at this point: It was a divisive president’s first midterm election and a surge of new candidates emerged from the other party, vowing to wrestle back power from a Washington under one-party control. That 2010 midterm election ended with 58 incumbents out of office — the most in recent history.

If the same number lose this year, it would likely bring the average House member’s experience down from 9.4 years in office to 8 years. This would be the lowest it’s been since the late 1990s.

2. The total number of vulnerable Republicans lose their seats: 22 losses

Even without predicting exactly who would be defeated, we can look to the number of vulnerable House Republicans as an indicator.

As of now, there are 22 Republicans incumbents running in districts that Inside Elections editor Nathan L. Gonzales has deemed neither safe nor likely to go in favor of the incumbent.

If that many lose re-election, it would push the average House member’s experience down to about 8.7 years — the lowest average since 2001, although very similar to the House experience level of the last Congress of President Barack Obama’s time in office.

3. Only the number of “toss-up” incumbents lose: 3 losses

If most Republicans running for re-election dodge the avalanche that seems to be coming for them this year, the average House member’s experience in the next Congress will be only slightly lower than the current one. Only three incumbents running — Republicans Jason Lewis of Minnesota, Will Hurd of Texas and Barbara Comstock — are in districts rated as tossups.

If just three members lose their races, the average experience could drop from 9.4 to 9.1 years. That would be very similar to the result if no members lost, since the average experience is already on track to drop because of the number of announced retirements and resignations. But it’s also a very generous outlook for how incumbents, especially Republicans, will fare in November.

Why this matters

The consequences of a surge of new blood could go a couple ways, depending on how the rest of this election season plays out.

The tea party wave of 2010, for example, brought in a cadre of House freshmen with less regard for the status quo or leadership’s way of doing things. Those members eventually contributed to the ouster of Republican Speaker John A. Boehner of Ohio and the primary defeat of Majority Leader Eric Cantor of Virginia, and generally made it more difficult for the chamber to pass moderate bills.

It’s too early to tell whether Democrats hoping to ride the post-2016, anti-Trump fervor to victory are more in line with the party and its congressional fundraising arm, the Democratic Congressional Campaign Committee. If they come to power with help from the DCCC and big party fundraisers, it could help guarantee California Rep. Nancy Pelosi would return to the speaker’s chair.

If, however, Democrats find success in traditionally Republican districts by attacking their cohorts in Washington, it could usher in a tea party-esque insurgency to the chamber.

“A lot is going to depend on how much they feel they owe their electoral success to the party,” said Lee Drutman, a senior fellow at the New America think tank who’s written about the large number of Republicans leaving Congress. “When you have new blood coming in, you have people who are not as wedded to the status quo and how things have been.”

One known effect of all these congressional departures will be a record number of vacancies for committees’ top Republicans.

Eight House committee chairmen, many of them term limited by Republican caucus rules on chairmanships, plan to retire at the end of this Congress. Another three have already left their posts, including two departures from the top spot on the Budget Committee since the beginning of 2016.

These exits, both at the committee and representative level, would likely lead to departures for long-term staff — furthering the legislative brain drain.

No matter the outcome, one certainty is that the House in the next Congress will be less experienced than the current one.