Democrats are going to win back the House this year. Just ask anybody. Even one of Senate Republican leader Mitch McConnell’s top outside allies says so.

“Our donors will often say we need to do everything we can to hold on to the Senate because there’s a chance we may not be able to hold the House,” Steven Law, who leads a Super PAC called the Senate Leadership Fund, told the Washington Post this week.

The conventional wisdom is solidifying that Democrats — buoyed by an unpopular President Donald Trump, an energized Democratic base, ample opportunities for pickups, and the historical rule that voters punish the party in the White House — will win the 20 or so seats they need to flip the House and maybe even get the Senate. It was the not-so-subtle subtext of House Speaker Paul Ryan’s announcement that he will leave Congress next year.

Of course, it’s not in the bag: A lot can happen between now and November, never mind that Senate Democrats are at an extreme disadvantage, that gerrymandering can curb the generic ballot by a lot, meaning there are plenty of R+whatever districts. Democrats will also remind you that Republicans are going to dramatically outspend them.

Democrats are nothing if not pessimists, after all — and they can come up with a whole lot more reasons to be worried this fall. I called up Democratic operatives with experience assessing the national congressional campaign landscape. I wanted to know: What keeps you up at night?

A lot, it turns out.

Fear 1: people decide the economy is good enough

Many of the economic indicators are strong. The unemployment rate is low (4.1 percent), wages are actually growing (at the fastest pace since 2009), and consumer confidence is strong (the highest since 2000). The structural problems in our economy — namely, income inequality — still exist, and not every part of the country is enjoying equitable growth. But things are mostly pretty good.

Yet Trump is broadly unpopular: He is 13 percentage points underwater, according to the RealClearPolitics average. As Nate Cohn wrote at the New York Times, the president is a historic outlier: We’ve almost never seen a president this unpopular when the economy is this strong.

So it’s sort of Chekhov’s economy for Democratic strategists. They’ve known about this incongruity for a while. What if voters wake up to it too?

“You worry that the economy continues to do well and there are enough voters that say, ‘You know, I’m okay. President Trump’s tweeting is annoying, but it doesn’t really bother me that the Republican Party isn’t holding him accountable,’” one Democratic operative working on the House races this year told me. “That is my biggest fear: You aren’t able to convince enough people that you need a Democratic Congress to keep this guy in check.”

This operative is thinking about historically Republican districts — the Texas suburbs, conservative enclaves in the Californian suburbs — where the repulsion for Trump should give Democrats an opportunity. Voters who have a pretty stable life but find the president, his style, and maybe some of his nativist tendencies unappealing.

The midterm electorate is already usually older, whiter, and more likely to vote Republican. The concern many Democratic strategists have is that those voters look around, decide they’re doing okay and their taxes have been cut at least a little bit, and eventually come home to Republicans. Trump isn’t enough to stop them checking a different box on Election Day.

As political scientist James Campbell once put it: “Campaigns remind Democrats why they are Democrats rather than Republicans and remind Republicans why they are Republicans rather than Democrats.”

And the US Chamber of Commerce and other outside groups are going to work their damnedest to try to rehabilitate the GOP tax bill with voters using TV ads.

“When his approval ratings have ticked up a couple of points, it’s because Republicans are less embarrassed to be Republicans,” the operative said.

Fear 2: something goes wrong with the candidates

Let’s get one thing out of the way: Bad candidates can win in the right circumstances.

“In 2006 and 2008, and on the Republican side in 2010, a lot of people got elected who did not run the best campaigns and who beat good opponents of the opposite party,” another Democratic strategist told me. “If the wave is big enough, it doesn’t actually matter.”

Nevertheless, in my conversations, I picked up on some level of concern that Democratic congressional candidates could hurt their own chances. Broadly speaking, the most comfortable place for an opposing-party candidate is, well, in opposition: Trump has let you down, and I will hold him accountable. Anything that changes that dynamic is a risk.

There was some internal debate in my conversations about what exactly the danger is.

Some strategists worried about nominating overly progressive candidates in more moderate suburban districts, where fiscally conservative voters might be spooked by a candidate who supports, say, Medicare-for-all.

“If you’re going to win these suburban swing districts, show them you’re not another tax-and-spend Democrat,” argued one strategist with this outlook. “If you’re in a battleground district, you should not be making a point. You should be trying to win your election.”

But others were more dismissive of those concerns. They came back to the election environment inevitably being defined more by Trump than the granular policy positions of the Democratic candidates.

Yet some of those operatives had another parallel concern: The record number of first-time candidates raises the risk of an unforced error — a gaffe, an unvetted skeleton in the closet, what have you — that redefines the race and makes it about them instead of Republicans. In the era of the #MeToo movement, allegations of past misconduct are harder to keep buried.

“We just have a bunch of first-time candidates. That brings an unknown risk,” said an operative with this concern. “Running for office is one of the most grueling experiences you’ll ever go through. None of them are probably ready for what’s about to come.”

But that also invited some pushback from still other strategists. As Trump himself proved, being a political neophyte can be an asset when the electorate is disillusioned with politics.

The precise nature and size of the candidate risk is up for debate. If the wave is big enough, it’s not going to matter. But when you spend your nights tossing and turning and wondering what could go wrong, you’re going to worry about one of your nominees making an unnecessary mess.

Fear 3: some act of God introduces an unknown variable to the campaign

This is the most uncomfortable electoral variable to discuss and the one you can plan for the least. You can try to craft a political message that keeps voters dissatisfied with Trump. You can do your best to vet your candidates and prepare them for the grind of a campaign.

But there are some things you simply cannot anticipate: a terrorist attack, an international crisis, a natural disaster, or a war.

It’s difficult to begin to quantify what the electoral repercussions would be in such big and unpredictable events. Some of the operatives just shrugged their shoulders when this point came up. What can you do? Black swan events are always a risk — and rarely an actual factor — in politics.

But a few were willing to at least talk through the electoral implications. Take a military intervention: Some Democrats argued that there is actually reason to think that could hurt Republicans as much as help. Trump’s brinksmanship with North Korea has been polarizing. The same would likely prove true for any military adventures the president decided to undertake in the next few months.

“Trump is so polarizing that unless America were attacked, it would be polarizing,” one strategist said. “Trump doesn’t get the benefit of the doubt. You’d have as many opponents as supporters.”

But conversely, there is the truism that Trump has yet to face an unmanufactured crisis during his presidency (well, excepting a couple of hurricanes and the widely criticized response to the crisis in Puerto Rico). While it could certainly turn out that he would bungle it and thus reinforce the perceptions that have made him so unpopular to begin with, there is also at least the possibility that he would handle it well and give Americans new confidence in his leadership.

As Vox’s Andrew Prokop wrote during the 2016 campaign, there is some scholarly evidence that the more hawkish party gets an electoral advantage when the unthinkable happens:

Experimental and real-world studies have tended to show that in the US and abroad, the major party with a more hawkish reputation usually benefits when international terror becomes a major concern. For instance, [Michael] Koch, Laron Williams, and Jason Smith studied how quickly various parliamentary governments lost their majority coalitions after transnational terrorist attacks in a 2012 paper. What they found was that right-leaning governments had an easier time holding on to power than left-leaning governments did. It seems the left gets more blame for terrorist attacks that occur under its watch.

“Trump hasn’t dealt with an actual crisis yet. If a legit crisis happens between now and November, how Trump handles it could shape how people view him and his presidency,” said yet another Democratic operative. “If he does well, that’s the kind of thing that could make people normalize his presidency.”

Don’t lose sight of the fundamentals. Trump’s unpopularity and the midterm factor should be winds at the backs of Democrats. Gerrymandering and a money disadvantage will likely make the lift a little more difficult.

But if you’re looking for X-factors in the 2018 midterms, this is what’s on the minds of the people whose job it is to worry.