(CNN) —  

On Tuesday in North Carolina, voters will pick their new member of Congress in the 9th District. While it’s only a single House seat and will have little obvious impact on the majority math for either party, there’s real reason to believe that what happens in this suburban Charlotte district could well change the course of the fight for House control next November.

Here’s why: On paper, this should be an easy victory for Republican state Sen. Dan Bishop. A Democrat hasn’t held the 9th District since the early 1960s. President Donald Trump carried it by 12 points in 2016. Bishop is a totally credible nominee with no disqualifying issues.

And yet, the race between Bishop and Dan McCready, the Democrat who lost the deeply controversial 2018 race for the seat, is, by all accounts, very close – with both national parties spending heavily – upwards of $10 million total – to get their preferred candidate across the line. That closeness explains why Trump himself traveled to the district on Monday night, imploring voters to “send a clear message to the America-hating left” by electing Bishop.

If Bishop wins – even if the margin is significantly narrower than Trump’s in the district – Republicans will breathe a massive sigh of relief and live to fight (and maybe win) another day.

But if Bishop loses, look out. What has been a low-lying dread creeping through the House Republican conference – typified by the dozen GOP members who are retiring with no other future political plans in place – will transform, quickly, into total panic.

Why? Because as I noted, this is a solidly Republican district. In fact, according to figures from the Democratic Congressional Campaign Committee, there are 34 districts currently held by Republican members of Congress that Trump carried by less than he did North Carolina’s 9th. (By contrast, Democratic incumbents only represent three districts where Trump won by more than he did this seat.)

If you don’t think every single one of those 34 GOP members are watching the North Carolina race extremely closely, then you are, in a word, wrong. Congress is a lot like high school – everybody is watching everybody else. There are no secrets. And everything that happens is immediately seen through that most human of lenses: “What does this mean for me?”

Now. There are some mitigating circumstances here. After all, the reason this seat is currently vacant is that the North Carolina Board of Elections refused to seat Republican Mark Harris after a 2018 election in which significant evidence of absentee-voter fraud occurred. Although Harris is not the party nominee – and Bishop has nothing to do with the fraud – there could be a lingering brand issue for Republicans.

That is a factor in this particular race that, clearly, won’t be replicated around the country for Republicans trying to hold their House seats in 2020.

But try telling that to already skittish Republican House members who have spent the past week watching Trump make a political hash out of Hurricane Dorian’s path and are confronted this morning with new polling from The Washington Post and ABC News that showed the President’s approval rating at a dismal 38%.

A loss in North Carolina on Tuesday night would almost certainly be a final straw for some House Republicans wavering about whether or not to run again in 2020. Confronted with the very real possibility that they could lose their seats in an environment in which Trump’s unpredictability is driving voters away from the party more broadly, retiring on their own terms might suddenly look much more appealing.

Already the retirements within their ranks have made House Republicans’ push to retake the majority in 2020 more difficult. A Bishop loss – and the potential panic that would cause among GOPers in Congress – could end or, at the very least, badly curtail Republican hopes before we even get to 2020.