From Jim Newell’s post, “The Class of Trump: Why Democrats feel so comfortable trying to expand the 2018 map” at slate.com:

The Democratic Congressional Campaign Committee is getting bolder. On Monday it announced 20 new districts it would target for recruitment and potential investment, raising its total target list to 79 districts. The initial round of 59 targeted districts, announced in January, took care of most of the perennial low-hanging fruit, but this new one cuts into some ambitiously red districts…The average rating of the 20 new districts, using the 2017 Cook Partisan Voting Index figures, is R+7.8. In a normal year, a host of districts like that are not worth much time, investment, or recruitment.

..Passage of the American Health Care Act opened new frontiers for Democrats. Representatives from each of the new districts voted for the AHCA, which would use nearly $1 trillion in Medicaid cuts to finance tax cuts for the wealthy. The health care bill itself is just an amuse-bouche for the party’s chief agenda item: additional tax cuts for the wealthy and corporations. You don’t have to like Democrats to hate this.

Newell notes a couple of other issues that are encouraging Democrats, including a campaign funds scandal anbd involvement in the Trump-Russia mess, but cautions that “The list is aspirational. Not all of the Democratic challengers for all of these districts are going to get all of the DCCC’s money and support.” He also cites retiring Republican House members and the emergence of some promising Democratic recruits joining the 2018 fray.

At The Hill, Ben Kamisar and Lisa Hagen affirm the same key reasons for improved democratic prospects in the House:

Democrats are increasingly bullish about the prospect of a wave election in 2018 amid backlash against the passage of the House GOP’s ObamaCare replacement bill and the snowballing revelations coming out of the White House…“Anyone who thinks the House isn’t in play is kidding themselves,” a former GOP aide told The Hill…The House healthcare bill is full of landmines and the constant White House drama Republicans have to defend is destroying any ability we have to be on offense or talk about a positive message.”

Kamisar and Hagen note further,

Democrats are, on average, leading Republicans by 7 points when voters are asked which party they prefer in the upcoming elections, according to Friday’s RealClearPolitics average…That average didn’t include a recent Quinnipiac University poll that put Democrats up by 16 points when participants were asked which party should win control of the House in 2018.

The Cook Political Report moved ratings for 20 House districts in favor of Democrats following the healthcare vote in the House, while Sabato’s Crystal Ball did the same for 18 districts in the days after that.

In their Politico post “Paging Rahm: House Dems revive 2006 playbook for 2018: The party is reviving the strategy it used the last time it took the House 11 years ago, but a lot has changed since then,” Edward-Isaac Dovere and Gabriel Debenedetti write:

..Democrats see the same ugly storm forming for Republicans that delivered them the majority 11 years ago, and they’re digging out the blueprint…The party is vastly expanding the number of districts it plans to contest, recruiting veterans and business owners to compete in conservative terrain as it did back then. Three senior House Democrats are soon heading to Chicago to seek advice from Rahm Emanuel, the party’s 2006 master strategist. Minority Leader Nancy Pelosi (D-Calif.) has been tutoring members on the party’s campaign efforts that year.

…Still, a lot has changed for Democrats since 2006, mostly for the worse, so re-adopting the campaign tactics from that year alone probably won’t cut it. For starters, Democrats need 24 seats to take back the majority vs. 17 seats to make up in 2006. The 2010 redistricting tilted the House landscape toward Republicans, putting more seats even further from Democrats’ grasp. And there’s a year-and-a-half to go in the most unpredictable environment in modern political history.

…This cycle, the Democratic Congressional Campaign Committee is investing early in research into Republican incumbents, diving deep into their records and histories for possible corruption and other liabilities, in hopes of promoting a narrative they then can tie to suspicions about Trump’s self-dealing…“Ethics,” said DCCC Executive Director Dan Sena, “will play a significant role.”

With nearly 18 months to go, Democratic candidates have good reasons not to get overconfident. But there are equally-good reasons for optimism — and for investing resources in promising candidates.