It makes perfect sense, really: When a midterm election is downhill for one party, it's easy for things to go really downhill. Donors on one side get enthusiastic, while on the other they get despondent. One side gets excellent recruits because it's a good year for its side; the other side gets the dregs. With enthusiasm comes high turnout in the primaries (which is likely to mean high turnout in the general election), while the other side finds it tough to drag people to the polls. That seems to be happening in this year's midterms, according to the Cook Political Report's David Wasserman:

"For Republicans, the 2018 House playing field is a lot like a game of Whack-a-Mole: everywhere they turn, new problems keep popping up in surprising places. In January, we rated 20 GOP-held seats as Toss Ups or worse, including three leaning towards Democrats. With today's changes, we now rate 37 GOP-held seats as Toss Ups or worse, including 10 leaning towards Democrats.

"Republicans are relieved that state Sen. Troy Balderson appears to have eked out a win in Ohio's 12th CD special election last week. But a new round of polls shows several more GOP incumbents, including Reps. Mimi Walters (CA-45) and Tom MacArthur (NJ-03) highly vulnerable. Their seats, along with Rep. Robert Pittenger's open NC-09, move from Lean Republican to the Toss Up column."

Walters is in Orange County (for decades hostile ground for Democrats). It's the typical upscale suburban district that goes from country-club Republican to mainstream Democrat in the Trump era. ("This wealthy southern Orange County district voted for Hillary Clinton 49 percent to 44 percent after voting for Mitt Romney by 12 points in 2012.")

In addition to those 37 Republican-held seats that are now Toss-Up or worse for the GOP, there are 25 Republican seats that are only "Lean Republican." That's a total of 62 seats that Republicans have a decent chance of losing. It can lose only about a third to keep the House majority.

Contrast that to the Democrats, who have a grand total of four seats rated Toss-Up or worse. Democrats can pick one or two to pour money into - or let them go by the wayside as they nudge more Republican seats in their direction.

While individual races might slide one way or another, it's hard to see what event would suddenly shift the midterms in Republicans' direction. The economy isn't going to radically change between now and Election Day (unless there is some event that precipitates an economic crisis). The GOP-led House and Senate aren't going to do much of anything between now and Election Day, so they cannot count on getting a boost from their legislative "accomplishments." (By the way, can you recall a less productive year for the House?)

By contrast, it's not impossible to imagine things might get even worse. Former aides (with tapes!) could pop up; Michael Cohen or other Trump associates might strike a plea deal. The trade wars could ratchet up, increasing pain in rural America, which depends on exports. And then there is health care, which is the driving issue for many Democrats and Democratic-leaning independents.

Red states are currently litigating to invalidate the Affordable Care Act, a reminder that the GOP has sought to push the ACA into the grave with no alternative. Andy Slavitt, former head of the Centers for Medicare and Medicaid Services, observes that the states (unopposed by the Trump administration) will be arguing to get rid of Medicaid expansion covering 12 million people, protection for pre-existing conditions, guaranteed coverage on parents' insurance up to age 26, the ban on lifetime limits, etc. Oral arguments are set for Sept. 10. Mark your calendars − I'm sure Democratic gubernatorial, House and Senate candidates will as they make the argument that Republicans want to "take away your health care." In this case, they'll have a point.

Jennifer Rubin writes the Right Turn blog for The Washington Post, offering reported opinion from a center-right perspective.