For Democrats to pick up the 24 seats they need to get a majority in the House, they probably need to win about 54 percent of all major-party votes cast.
News analysis
WASHINGTON — Democrats ended 2016 dejected and despondent after Donald Trump shocked Hillary Clinton — and the world — by a tiny combined margin of 77,744 votes in Michigan, Pennsylvania and Wisconsin to win the presidency.
A year later, Democrats are ending 2017 as the slight favorites to take back the House in the midterm elections, thanks to a surge of grassroots anti-Trump activism and an explosion of credible Democratic candidates.
It's an extraordinary turn.
For years, I've argued that House Republicans' twin geographic advantages — their dominance in the 2011 round of congressional districting and Democratic voters' tendency to cluster in cities and waste their own votes — meant that to reclaim the majority, Democrats would either need a resettlement program of their own voters or an unpopular GOP president in a midterm year.
The latter has come true. Trump's poor standing — just 41 percent approval in the most recent NBC/WSJ poll — have propelled Democrats to leads in voters' preference for Congress that may be too large for GOP gerrymandering to withstand.
For Democrats to pick up the 24 seats they need to get to the narrowest possible majority of 218 seats, they probably need to win about 54 percent of all major-party votes cast for the House. That's because in each of the past three elections, Republicans have won a four percent greater share of House seats than votes (for example, in 2016 they won about 51 percent of the vote but 55 percent of seats).
As 2017 draws to a close, the balance of polls suggests Democrats are narrow favorites to hit those thresholds; in fact, Democrats' main problem is that November is still more than 10 months away. In my view, five factors help explain this moment:
1. Demographics
Trump's upset was powered by white voters without college degrees. The problem for Republicans? Voters without college degrees have a dismal track record of voting in off-year elections. This is similar to the problem Obama had: His base of young and non-white voters also had a terrible history of showing up in off years. That didn't change after he took office, and it cost Democrats dearly in 2010 and 2014.
Simply put, 2018 is on track to be the "Year of the Angry White College Graduate." I'd estimate the college-educated share of the electorate will be around 43 or 44 percent next year, up from 39 percent in 2016. That's dreadful news for Republicans: These voters have indicated the highest intensity of opposition to Trump in polls, and we've already seen them power Democrats to victory in Virginia and Alabama.
2. No Leader? No Message? No Problem
Democrats' congressional leaders, House Minority Leader Nancy Pelosi, D-Calif., and Senate Minority Leader Chuck Schumer, D-N.Y., are old-school coastal liberals with plenty of skeptics in their party's ranks. Between the likes of Bernie Sanders, Joe Biden and Elizabeth Warren, there's no consensus frontrunner for the 2020 nomination. And Democrats' "Better Deal" agenda isn't exactly brimming with groundbreaking new policy ideas.
If you're looking for one person who unites today's Democratic Party, it's probably not a Democrat: It's Donald Trump. When you're the party out of power, not having a clear leader can be an advantage — just ask the Republicans who won in 2010 by running as change agents and were the faces of their party in each state and district. For Democrats, a leadership vacuum is a problem for 2020, not 2018.
3. Check and Balance Voters
According to 2016's exit polls, 19 percent of voters had an unfavorable view of both Trump and Clinton. Down-ballot, these voters preferred Republican congressional candidates 63 percent to 33 percent. A likely reason? Most went to the polls believing Clinton would win the election, and voted for their local GOP candidate believing he or she would be a "check" on Clinton's power in the White House.
In 2018, this dynamic is working in the opposite direction. These voters still don't like Trump, but in a midterm there's no doubt as to the occupant of the Oval Office. Now, they may be inclined to vote for a Democrat as a check on Trump's power — and that might help explain why independents favored Democratic control of Congress by 12 points in the most recent NBC/WSJ poll.
4. History
Midterm elections tend to strongly favor the party out of the White House. The president's party has lost House seats in 35 of the 38 midterm elections since the Civil War. In midterms when the president's approval rating has been lower than 50 percent, the president's party has lost an average of 40 House seats — far more than the 24 Democrats need for the majority in 2018.
Of course, Republicans benefit from the fact there are far fewer competitive House seats than there used to be. Thanks to voters' self-sorting and redistricting, the number of "swing seats" has declined 56 percent since 1997. However, Trump's approval rating is also lower than Bill Clinton's was when Democrats lost 52 seats in 1994 and Obama's was when Democrats lost 63 seats in 2010.
5. Enthusiasm Gap
The adage most applicable to midterm elections? "Anger is a stronger motivator than love." Just as voters who disliked Obama were much likelier to show up in 2010 and 2014 than his supporters, those angry with Trump are much likelier to vote in 2018 than voters who are happy with the status quo. We've seen this dynamic again and again in 2017's special elections.
Some of the most worrisome signs for Republicans have been the stark turnout differentials between red and blue precincts. In Virginia's gubernatorial election, turnout was up 20 percent over 2013 in blue localities versus 13 percent in red localities. And in the six special congressional elections held in 2017, Democrats have averaged 71 percent of Clinton's 2016 votes, while GOP candidates averaged just 55 percent of Trump's 2016 performance.
David Wasserman, House editor for The Cook Political Report, is an NBC News contributor and senior analyst with the NBC Election Unit.