Since 1938 is the short answer. What might that translate into come November? That's a tricky question, even if the GOP's standing remains historically strong into the fall. Let's think about more recent history. Back in 2010, Republicans gained 63 seats in a political pulverization for the ages, as voters' backlash against Barack Obama and unified Democratic governance (exemplified by Obamacare) swept the depleted opposition back into a House majority. Republicans netted five Senate seats that cycle, too, but still remained in the minority because Democrats enjoyed a massive majority in the upper chamber after 2008. In fact, they commanded a filibuster-proof 60-40 majority for a period of time.
In 2014, another Obama midterm, Republicans maintained their House majority, expanding it by a relatively modest 13 seats (up to a substantial 247). The bottom really fell out for Democrats on the Senate side that year. The House GOP didn't have too much room to grow; the Senate GOP did. And they took advantage, gaining nine seats in one fell swoop. The swing was wild – a 20-seat Democratic majority in 2009/10 to an eight-seat Republican majority by 2015. But according to this CNN analysis, the GOP's poll standing ahead of the 2022 midterms is currently even more robust than it was ahead of 2010 or 2014. As mentioned above, this CNN analysis finds that you'd have to go back to before World War II to find a political environment more hospitable for the party:
“Republicans lead on the issue that’s most important. No wonder they have a historic advantage on the generic congressional ballot.” @ForecasterEnten reports on the grim outlook for Democrats in November pic.twitter.com/V4CTFSZzok
— The Lead CNN (@TheLeadCNN) June 6, 2022
What happened in 1938, by the way? Republicans gained eight Senate seats, 12 governorships, and 80 House seats. Republicans aren't in deep enough holes to touch any of those numbers this year, but gaining a few dozen House seats, netting a few Senate seats (they only need +1 to reclaim a majority), and at least holding serve on governorships (they hold 28 right now, to Democrats' 22) seems eminently achievable under these circumstances. As Enten points out in the clip, the only circumstances under which the incumbent president's party hasn't lost a decent chunk of seats in a midterm election since WWII entails a very popular president enjoying soaring approval ratings. That...is not the case right now. At the tail end of the video above, Biden's standing on the economy is shown to be in dead last place, compared to all modern-era presidents, at this point in their respective presidencies. He's tied for dead last with Jimmy Carter. There's that name again.
But could the Democrats still turn things around? After all, it's June, not October. Theoretically, yes. Anything can happen, and the ruling party's fortunes could potentially marginally and steadily improve over the coming months, averting a wipeout (in this case, their best-case scenario seems to be losing the House by a manageable margin, and clinging to the narrowest of Senate majorities). That's possible. Is it likely, based on the present climate, coupled with history? No, it is not, as Henry Olsen recently explained (via Allahpundit) in the Washington Post:
Recent political history shows that the course of a fall election is almost always set by Memorial Day. RealClearPolitics Senior Elections Analyst Sean Trende recently noted that “election outcomes are more-or-less baked in” by the end of the second quarter of an election year. Not even the financial crash of 2008 made a significant dent in that year’s outcome, which Trende says was largely expected in May of that year. One probably needs to go back to the Cuban missile crisis of 1962 to find an event that might have significantly helped the party in power on the eve of a midterm vote...Political waves also take predictable courses, and the final outcome is almost always worse for the losing party than analysts predicted six months out. In May 2010, the Rothenberg Political Report (now Inside Elections with Nathan L. Gonzales) projected a big Republican year, with GOP House gains of two to three dozen seats. Their final pre-election forecast predicted gains between 55 and 65 seats. The GOP ultimately picked up 63 from Democrats.
Well, Memorial Day is now in the rearview mirror, and we're approaching the end of that second quarter, referenced by Trende. Where do things stand at the moment? Republicans lead by two points, on average, on the generic 2022 ballot. If the final outcome turns out to be "worse for the losing party than analysts predicted six months out," the pain for Democrats could be dramatic. On that point, I'll leave you with this comparison: The final RCP generic ballot average in 2014 (one of the aforementioned red wave years) had the GOP ahead by roughly two points. They proceeded to win by nearly six points and attained a commanding position in the House, plus a sizable majority in the Senate. Nobody should count any chickens, etc. – but there's reason to believe a bad outcome is already "baked in," and a further deterioration in the party in power's standing might be more likely than an improvement.