California U.S. representative Steve Knight is one of 14 Republicans who voted for Trumpcare even though Trump lost their districts in 2016. Photo: Rich Pedroncelli/AP

It is generally assumed that passage of the American Health Care Act by the U.S. House yesterday could prove to be a handicap for House Republicans collectively in 2018, much as Obamacare was for Democrats in 2010. But it may be a very individual problem for the 14 House Republicans who voted for the toxic health-care bill and who represent districts won by Hillary Clinton in 2016. And more broadly, the 46 pro-AHCA members from districts that voted for Clinton in 2016 or for Obama in 2008 or 2012 could represent a potential pool of seats Democrats might target in their drive to gain the net 23 or 24 (depending on what happens in GA-06 on June 20) seats they’d need to retake the House.

Not coincidentally, House election expert David Wasserman of the Cook Political Report put out a new set of 2018 race ratings the day after the AHCA vote, which shifted no fewer than 20 contests in a pro-Democratic direction, including four that became toss-ups and eleven that moved from “Likely Republican” to the much more competitive “Lean Republican.”

Although it’s the first of potentially many explosive votes, House Republicans’ willingness to spend political capital on a proposal that garnered the support of just 17 percent of the public in a March Quinnipiac poll is consistent with past scenarios that have generated a midterm wave.

Indeed, you can already see the preconditions for the wave building. In March, Wasserman listed only 12 Republican seats that were anything less promising for the GOP than “Likely Republican.” That number is now up to 25. If this trend continues — perhaps enhanced by GOP retirements like that of Ileana Ros-Lehtinen last week — the majority party’s grip on the House could further weaken.

As Wasserman notes, the growing mood of Democratic optimism about 2018 is doing something else that could make more and more contests competitive — bringing in a bumper crop of Democratic candidates:

Democrats aren’t so much recruiting candidates as they are overwhelmed by a deluge of eager newcomers, including doctors and veterans in traditionally red seats who have no political record for the GOP to attack — almost a mirror image of 2010.

Without question, if there is a Democratic House wave in 2018, it will first appear on the Pacific coast in California. Seven House Republicans representing California districts that Clinton carried voted for Trumpcare, which could be an even greater problem than elsewhere in a state where Obamacare has run smoothly and there is a long history of popular support for the state’s robust Medicaid program.

Representative Darrell Issa, who won the last House race to be decided last November, is one obvious Democratic target. But in some ways the most representative figure is California colleague Steve Knight, who represents a rapidly suburbanizing and increasingly diverse high-desert district in Los Angeles and Ventura Counties. Knight won an expensive 2016 race by 6 points even as Clinton carried the district by 7 points; he refused to say he would vote for Trump, which will not help him with Trump loyalists. More to the point, Democrats are avid to take him on; 2016 candidate Bryan Caforio may run again, but the more interesting prospects are two young women who are political novices: volcano geologist Jess Phoenix and the executive director of a statewide program for the homeless, Katie Hill.

Wasserman already shows the Issa and Knight races as toss-ups, with the five other California Republicans in districts Clinton carried rated as “Lean Republican.” It would be wise to watch all these Golden State districts closely for signs of a 2010-style tsunami, but this time moving in the opposite direction.