The math just didn't work: Democrats would have to win three seats. There are only two good pick-up opportunities on the map -- Arizona and Nevada. And their incumbents are defending 10 seats in states President Donald Trump won.
The House could be won if there is a big anti-Trump turnout, and Democrats hope to pick off governor's offices and state legislatures. But the Senate, they thought, would have to wait for 2020.
Alabama could change all that.
The Washington Post's report
that Republican nominee Roy Moore alleged pursued teenage girls while in his thirties -- which Moore denies -- has led to a chorus of GOP senators conditionally calling on Moore to withdraw from the ballot ahead of the December 12 special election for Attorney General Jeff Sessions' old seat.
"If these allegations are true, he must step aside," Senate Majority Leader Mitch McConnell said.
"The allegations against Roy Moore are deeply disturbing and disqualifying," said Sen. John McCain, R-Arizona. "He should immediately step aside and allow the people of Alabama to elect a candidate they can be proud of."
Moore has given no indication that he'll do so. Alabama law doesn't allow for him to be replaced on the ballot at this stage, anyway. Sen. Lisa Murkowski, R-Alaska, said she talked to Sen. Luther Strange -- the Alabama Republican temporarily appointed to fill Sessions' seat, who lost a primary to Moore -- about running as a write-in candidate.
Moore was already on the record advocating discrimination. He has said homosexuality should be illegal and once wrote that Muslim people shouldn't be allowed in Congress. Those comments plus his removal -- twice -- as Alabama state Supreme Court chief justice has helped Democrat Doug Jones so far run a closer-than-expected race in a deep-red state.
It's not yet clear how badly these allegations will damage Moore.
But there are three things you should know:
1. After Tuesday's blue wave through the Virginia suburbs, Democrats are already incredibly optimistic about the 2018 midterms.
2. Republicans face long, bitter primaries in nearly every state where they hope to knock off Democratic incumbents. And those Democrats haven't had to cast any tough, politically damaging votes since Trump took office.
3. Alabama represents the possible third seat -- the one more they had to have to try to win control of the Senate.
It's not Democrats' only shot at adding one more Republican-held seat to the 2018 battlefield. The party is trying to recruit former Gov. Phil Bredesen into the Tennessee Senate race to replace the retiring Bob Corker, and Rep. Beto O'Rourke hopes Texas will have moved left enough that his race against Sen. Ted Cruz might prove competitive.
But Alabama is now the race to watch. And since its special election is December 12 -- just a little more than a month away -- it won't take long to sort through the fallout of Thursday's bombshell.
As announced on Wednesday, Republican Gov. Kay Ivey is not endorsing Moore -- in accordance, her office said, with a self-imposed policy that began when she took the office in April -- but did plan to vote for him.
Asked by CNN Thursday, after the Post story was published, if Ivey would still vote for Moore, a spokesman for Ivey said he was unsure.
In a statement released later in the day, Ivey didn't address the question, but called the allegations against Moore "deeply disturbing" and said she would "hold judgment until we know the facts. The people of Alabama deserve to know the truth and will make their own decisions."