What's likely to happen?
To take control of the Senate, Democrats need to keep all the seats they now hold, and take two further seats, which is harder than it sounds. That's unlikely, by all accounts, because the map is so friendly for the GOP.
In the House, Democrats need a net gain of 23 seats. In the 2010 midterms, the Democrats, with Mr Obama in office, lost 63 seats.
President Donald Trump implored his supporters to vote on Tuesday, saying the media will treat the midterm results as a referendum on his presidency. If Democrats win the House, Trump will have a ready-made foil for his 2020 re-election campaign, even if his Democratic opponent is not such a lightning rod. A CNN poll gave Democrats the largest margin, a 13-point advantage; an NBC/Wall Street Journal poll had the Democratic lead at 7 points.
The Senate map for Democrats is brutal, however. "Just even the fact of it being so much, is it simply a matter that early votes have expanded?"
As part of that oversight, House Minority Leader Nancy Pelosi, D-Calif., has named a top priority: forcing Trump to hand over his tax returns. So many of those races are running through the suburbs, where independents and wealthy, college-educated women live, both of which have consistently in polling said they disapproved of the job the president is doing and prefer to vote for a Democrat in their district. Ryan seems to believe that the way to break the blue wave is to find those indies who are still left on the table, presumably by focusing on the economy. He has focused on the competitive Senate races the final days of his scorched-earth campaign blitz, and has distanced himself from blame should Republicans lose the House.
A slim Republican majority in the House would also present challenges, likely inflaming simmering intraparty disputes. Forty-five percent (45%) would vote for the Democrat.
The math in the Senate is better for Republicans. Heidi Heitkamp, a Democrat, in North Dakota. Thirty-six of 50 states will also hold elections for governor.
Sen. Heidi Heitkamp, D-N.D., speaks during a Senate Banking Committee hearing in Washington on May 24, 2018.
The Republican president has also been warning the other party will destroy a healthy U.S. economy if they win the keys to power.
Laying into the tangled legal scandals enveloping the Trump administration - especially the possible collusion between his presidential campaign and Russian operatives - Obama scoffed, "They've racked up enough indictments to fill a football team".
Linda Sarsour, a party activist and an organizer of the nationwide Women's March, which was fuelled by anger over Trump's 2016 victory, argued that Democrats must "unapologetically call out the president" while providing their own vision for the country. And it wouldn't be wrong.
"But radical Democrats want to turn back the clock for the rule of corrupt power-hungry globalists", Trump added. FiveThirtyEight has them at a 1-in-8 shot. There are only 9 Republican seats up for election. It wouldn't necessarily be a resounding affirmation of Trump - these are only red states the GOP would be winning - but it would lead to some real, justified soul-searching.
OneNewsNow is working alongside its sister organization, American Family Radio, to provide live election night coverage from Tim Wildmon, president of the American Family Association, and Fred Jackson, news director of American Family News, as well as other familiar AFA voices.
Her appearance, in a former Pottery Barn that San Francisco Democrats have transformed into an election war room, capped a cross-country campaign swing stumping for Democratic candidates and meeting activists.
In the Legislature, all 203 House seats are up, along with 25 Senate seats. What happens when they actually have power and the base wants them to go further than they think is prudent?
What it would mean: The same as above - chaos - except less specifically partisan. "We're not used to friendly crowds", Sanders said, before tailoring her message to a specific demographic.
ABC News' Political Director Rick Klein and Chief White House and Washington Correspondent Jon Karl spoke with Deputy Political Director MaryAlice Parks and Senior National Correspondent Terry Moran about what to expect on Tuesday on this week's Powerhouse Politics Podcast. A Minnesota native, he has also written about politics for the Minneapolis Star Tribune and the Hill newspaper.