Often, these departures involve members of the minority party, who have a frustrating, unpleasant Capitol Hill life lacking any real control over the legislative agenda.
Sure enough, that's happening again in the winter of 2018. But this time is quite different. This time it's the members of the controlling majority Republicans who are packing it in and in large numbers.
So far, a record 31 Republicans are quitting the House. That's 13 percent of the entire caucus and it's only January. Perhaps they sense a Democrat wave in November. Some are term-limited as committee chairs. Some simply tired of the hassle, the bitter partisan environment and perhaps this president.
The last time so many exits occurred was 1994, President Clinton's first midterm, when 28 Democrats left, followed by the wave election of Newt Gingrich's Republican Revolution.
The reasons for the latest exodus are varied and revealing, from burnout and the likelihood of defeat to ambition for higher office.
More importantly, this burst of individual departures taken together demolishes most political expectations for next November's midterm elections. Voters in modern times have preferred divided D.C. government, the White House held by one party, and at least one congressional chamber held by the other.
This would create, however, the environment for likely gridlock during the second half of President Trump's term with political bloodletting on an epic scale. It also would allow voters to grumble about nothing getting done in Washington.
If you thought 2017 was full of political turmoil with an unorthodox president who isn't really a Republican feuding with factions in the House and Senate that seem like several GOP parties, wait until Democrats get control of congressional committees with the power of subpoenas, investigations and even possible impeachment.
Historical patterns suggest Democratic gains on Nov. 6 that will hand the over-sized speaker's gavel back to a confused Nancy Pelosi and her aged team, all of which are over three-quarters of a century old. They've coasted these last 12 months largely free of alternate positive policies, save to embarrass and obstruct this White House and its Oval Office usurper.
In this era of hyper-partisanship, Democrats might even retake the U.S. Senate and stymie, for instance, all of Trump's judicial appointments, including expected Supreme Court nominees.
The GOP has only a one-vote Senate margin. So the Democrat caucus need gain only two seats for control. As it happens, however, Democrats must also defend 25 of the 33 seats up this time, a tall order even in normal political times, which these aren't.
A president is never on any midterm ballot. But any chief executive's first midterm elections are usually a referendum on the president's party and policies. The party controlling the White House typically loses around 30 House seats. Democrats need only gain 24 to oust Paul Ryan.
But midterm elections also typically have lower turnouts. Trump intends to campaign. Will that help or hurt? Will his hardcore core of supporters turn out and turn back an anticipated Democratic wave relying on unreliable turnouts by younger voters and minorities?
Will a stronger economy now perking along at three-plus percent growth before tax cuts and employer bonuses kick in ameliorate voter anger? And given all the disagreements Trump has had with congressional Republicans, will voters even see the New Yorker as a Republican Party leader to be punished?
Democrats are behind in money and have no leader or celebrity, save Barack Obama, to help rake in funds. During 2017, the Republican National Committee took in more than $130 million, twice what its Democratic counterpart raised. And most of the GOP haul came via small donations from first-time contributors. The money is going to reinforce the RNC's ambitious national ground game.
Democrats are preparing, too. They can rely on widespread Trump animus. But their state-level political farm teams have been decimated by Republican successes; the GOP now controls 33 governor's offices, 67 of 98 state legislative chambers and both houses in 26 states.
So, Democrats have launched an aggressive candidate recruiting drive focused especially on veterans and small business owners.
This has several advantages: One, such fresh-faced candidates are outsiders, as Trump was, unassociated with the reviled Washington political class and, importantly, with no previous policy positions or votes for opponents to assail. Veterans can also help address Democrats' perceived weaknesses on national security and the military.
Democrats are particularly aiming at the 23 House seats captured by Republicans but that are in congressional districts won by Hillary Clinton.
Of course, a lot can happen in the next 42 weeks. But at the moment Democrats are as supremely confident of election victory come November as Clinton was on Election Day 2016.
McClatchy Washington Bureau