But two years after an election that proved polls and prognosticators wrong, nothing is certain on the eve of the first nationwide elections of the Trump presidency. And it made clear the extent to which Trump has remade his party to his own specifications, as he suggested that those who survived were indebted to him, a president who prizes loyalty above all else.
"Tomorrow will be a new day in America", declared House Minority Leader Nancy Pelosi, who would be in line to become the next House speaker.
In that scenario, we'd be talking about the vast majority of those 30 toss-ups going to the Democrats, along with potentially some upsets in districts Republicans are expected to hold. "It is about restoring the Constitution's checks and balances to the Trump administration", Pelosi said.
And just look at how wide the playing field is - Democrats need to pick up 23 seats to take back the House, and they are targeting some 80 Republican-held seats.
For Democrats, a scenario where Republicans keep both chambers would be transformative, particularly given their confidence going into the election.
The marquee governor's race in Florida was a nail-biter, and it eventually went to the Trump-aligned Republican candidate Ron DeSantis, who squeaked past Andrew Gillum by about one percentage point. Ted Cruz in Texas. Now, Democrats are in control once again.
They won the House, which will change hands for the third time in 12 volatile years, by performing strongly in suburban areas where Trump's flaming rhetoric is toxic.
But with the party leading the House, Trump would be forced to compromise more - or risk presiding over an ever more divided country.
During the final stretch of the race, Trump tore across the country, holding 11 rallies over six days.
Former President Barack Obama - on the campaign trail for the Democratic party - said earlier on Monday that "the character of our country is on the ballot". Trump, who loves nothing more than to identify new enemies, will be a formidable opponent.
Secondly, it could lead to a string of damaging congressional investigations being launched by House committees controlled by the Democrats, on everything from Mr Trump's tax returns to the business interests of his family.
Democratic candidates for the House of Representative have raised $649m (£500m) from individual donors, more than doubling the $312m tally for the Republicans. That was rewarded, and what message would that send?
"The first thing [Republicans] will say the morning after the election is we are dedicated to the re-election of Donald Trump".
His ability to govern in the final two years of his term will hinge upon the outcome.
Cook said Democrats have a possibility of gaining as few as 20 seats and as many as 45 seats.
A total of 155 Republican incumbents are defending House seats in districts Trump won by double digits in 2016. Republican Sen. Dean Heller of Nevada, for example was defeated although he had embraced Trump, with both highlighting their desire to get more of the president's judicial nominees confirmed, a top priority for many social conservatives. Trump also helped topple another foe, Democratic Sen. Claire McCaskill is unable to hold on in Missouri.
Republicans rolled into the election with a 77-57 House majority. She is not running as a progressive firebrand, but just as Brat rode the Tea Party wave against Cantor, Spanberger could capitalize on the suburban backlash to the President in a traditionally Republican district.
The night's news wasn't completely disastrous for Democrats.
Add to the mix the against-all-odds confirmation of Supreme Court Justice Brett Kavanaugh in spite of high-school sexual assault allegations from the credible Christine Blasey Ford, and you have a powerful voting bloc capable of - and widely expected to - overturn the Republican majority in the House of Representatives. The fact that they are likely to win back a chamber that seemed so out of reach for the entire decade is big, in and of itself.
Democrats hoped their supporters' would surge to the polls.
What is next for Trump?
Many Democratic candidates in tight races shied away from harsh criticism of Trump, focusing instead on bread-and-butter issues like maintaining health insurance protections for people with pre-existing medical conditions and safeguarding the Social Security retirement and Medicare healthcare programs for senior citizens.
Fundraising, polls and history were not on the president's side.
Aides set up televisions in the White House residence for Trump, first lady Melania Trump and their guests to watch election results come in, with the sets tuned to different cable news channels.
Obama said Republicans were taking credit for the economic renewal that started under his presidency.
Almost two-thirds said Trump was a reason for their vote.
"He is really angry at Ryan", one source said, on "everything". All three and Sherrod Brown, a pro-labor senator victorious in OH, are considered potential 2020 Democratic presidential contenders.