The reverse is true for Republicans. They've spent the past six years or so ballooning their majorities to historic levels in state and congressional politics — so much so that they may have hit their max. Which means on Tuesday, down-ballot Republicans may have nowhere to go but down.
Of course, they won't have too far to fall. Republicans have such a big cushion in their majorities that it's going to take more than one great night from Democrats to turn a red America blue.
With Jacobson's help, let's run down some of the races where Democrats could eat into Republican majorities:
Lay of the land: There are only 12 governor's mansions up this cycle, and only six of them are competitive: West Virginia (D), New Hampshire (D), Indiana (R), Missouri (D), Vermont (D), North Carolina (R). (A seventh, Montana (D), gets an honorable mention for possibly being competitive.)
How much ground Democrats could make up: A good night for Democrats would have them cutting into Republicans' majority by a few seats, even unseating a sitting GOP governor.
But Republicans will still wake up Wednesday with majority control of governor's mansions. They currently hold 31 out of 50. The best-case scenario for them has them ending the night with 32-35, which would tie a pre-World War II majority. The worst-case scenario for Republicans has them holding 29, which is still a significant majority of governors' mansions.
Lay of the land: Let's talk specifically about the House of Representatives, since partisan control of the Senate is much more uncertain. In the House, Republicans currently hold a historically high 246-to-186 majority. But they may be a victim of their own success: They are holding 26 districts that Obama won not just once, but twice. In The Fix's latest House race rankings, nine of the districts most likely to flip are Republican held. That's one reason the House looks to be one of the best places for Democrats to regain some of the footing they lost in the Obama years.
What could happen Tuesday: The majority is probably out of reach for Democrats. To get it, Democrats would effectively have to run the table on competitive races, winning 36 of the 49 competitive districts. That would translate to winning every “lean Democratic” district and every “toss-up” district, as well as 9 out of 22 districts we currently rate as “lean Republican.” (The party that holds 218 seats holds the majority.)
How much ground Democrats could make up: The good news for Democrats is that there are so many races in play that even if they take just half of the seats we've ranked “toss-ups,” they'll have gained 13 seats and cut the GOP majority almost in half. A really, really good night for Democrats would be to pick up 20 seats. And our House rankings actually have Democrats doing close to that, predicting Republicans go down from a 246 majority to a 227 one.
Lay of the land: Here, too, Republicans have a huge cushion — but will actually be on defense because of it. They control 69 of the 99 chambers. (Well, technically they control 68. Nebraska's one legislative chamber is nonpartisan, but Republican in practice). Republicans have gobbled up so many state legislative chambers in the past few elections, they're defending 23 chambers in states Obama carried twice.
That's almost the exact opposite of the lay of the land leading up the 2010 election, where Democrats had a 2-to-1 advantage over Republicans in state legislative chambers. Now Republicans have a 2-to-1 advantage over Democrats.
Let's pause for a moment to talk about why party control of state legislative chambers has flipped so drastically in favor of Republicans. I talked to Jacobson in May about it, and he said it comes down to a few things, which we can also extrapolate out to governors and House races:
2) Redistricting after the 2010 Census. Republicans controlled a majority of state chambers when it was time to draw new state and federal district lines, and they drew a lot of races to make it harder for Democrats to win.
3) President Obama. The party that holds the White House tends to lose down-ballot. Jacobson said the losses have been particularly bad for Democrats during the Obama years (though not unprecedented). “Democrats could probably do better at the lower levels if a Republican candidate won the White House,” Jacobson said, “though I'm not sure they would want to make that trade-off.”
What could happen Tuesday: There are 26 competitive chambers, 18 Republican and eight Democratic. Jacobson estimated about six or so chambers could switch parties, maybe a few more if Clinton does really well on Tuesday. Some of those will go Democratic, some Republican. His full race ratings are here.
How much ground Democrats could make up: A really great election night for Democrats has them winning back seven to eight legislative chambers. Jacobson says to watch for which party takes the New Hampshire House and the North Carolina state House and Senate for any indications of a Democratic wave.
We'll likely wake up Wednesday with Democrats putting a small dent into Republicans' majority of state legislative chambers.
And that's really the story for down-ballot Democrats this cycle. They're shaping up to have a good election night in part because the last few have been so bad for them.
The Fix's Aaron Blake contributed to this report.