There is no shortage of numbers and developments that should be worrisome to Republicans as they approach the 2018 midterm elections. Democrats swept both of the 2017 gubernatorial races, in New Jersey and Virginia, captured a U.S. Senate seat in ruby-red Alabama, and scored strong state legislative gains across the country. While no special elections have shifted House seats from the Republican to the Democratic side, in the four GOP-held districts that theoretically could have changed hands, Republicans ran 8 points behind the party’s typical performance.

The Gallup Poll earlier this month showed a 5-point decline for Republicans in national party identification, while an NBC News/Wall Street Journal poll released Sunday indicated that Democrats now have an 11-point lead in the national generic congressional ballot test, 50 to 39 percent. This represents their biggest lead since September 2008, on the eve of Barack Obama’s presidential win and strong Democratic gains in the House and Senate. Should the generic hold at that level, shift in control of the House from Republicans to Democrats would be very likely. The Democrats would also likely make gains in the Senate, though not necessarily gaining a majority. That same NBC/WSJ poll showed that Democratic voters, by a margin of 10 points, were more interested in the midterms than Republican voters, which is consistent with what we saw in the recent Alabama and Virginia elections.

Political watchers in both parties who have analyzed past wave elections see warning signs of another one in 2018.

Some political professionals have suggested that allegations of sexual harassment on Capitol Hill, which seem likely to continue and possibly get far worse, might end up hurting both parties, potentially costing Democrats some momentum. The counterargument is that the party holding both House and Senate majorities tends to take the brunt of negative publicity, as evidenced by the House bank and post-office scandals that straddled both the 1992 and 1994 elections. Back then, Democrats controlled both the House and the Senate, and the scandals eventually hurt them far more than the GOP. They lost their House majority for the first time in 40 years, as well as their majority in the Senate, which they had controlled for 34 of the preceding 40 years.

With the Democratic victory in the special election in Alabama, the bar for taking the Senate now has dropped from three seats to just two—still unlikely but quite plausible. It is now reasonable to say that the Senate is in play for the first time this cycle.

So what could calm or even reverse the hurricane-force winds that are currently blowing from right to left? Before any election, there is always the possibility of a “Black Swan,” an unexpected development with seismic consequences that completely changes the political environment in the way that the attacks of Sept. 11, 2001 did. But short of such a Black Swan event, what could change things? If we are wrong about this current political climate, how are we wrong?

The only plausible theory that I can come up with is the economy. We have seen growth in gross domestic product for the last two quarters of 3 percent, and economic growth in the fourth quarter figures to be in the same neighborhood. Joblessness is down to 4.1 percent—pretty much full employment—and the stock market and consumer confidence are regularly hitting record highs. This raises a question about political gravity: How can economic factors be so good while President Trump’s job-approval ratings, currently around 36 or 37 percent, are the lowest of any newly elected president in the history of modern polling?

But what if the economy continues to grow at this pace through the November 2018 election? What if unemployment remains at such a low level, consumer confidence stays high, and people’s 401(k) retirement funds continue to grow? Would six quarters of a buoyant economy ease the disenchantment of Republican and conservative voters, the anger of independent and centrist voters, and the intensity of opposition toward both Trump and the Republican Congress among Democratic and liberal voters? Would the economy have ameliorative effects strong enough to save the GOP majority in the House and allow Senate Republicans to pick up Democratic seats in traditionally Republican states?

Remember when President Clinton was plagued with the Monica Lewinsky scandal and Republicans impeached him in the House and put him on trial in the Senate? The economy was strong, the country was doing well, and Americans decided to stick with him despite behavior that one could assume would have cost him the presidency under other circumstances. The strength of the economy was the major factor in saving his presidency. Could six quarters benefit Trump and his party in the way that it helped Clinton and his party 20 years ago?

I remain quite skeptical that this will happen, but in thinking about how the trajectory of this election could shift, this would seem to be the most plausible factor, and one to be monitored for changes in the political mood. Trump’s approval ratings, the number of voters identifying themselves as Republicans, and the GOP’s standing on the generic congressional ballot could be expected to rise if the political atmosphere changes. If it happens, we will know it when we see it. Otherwise, it is still advisable for Republicans to batten down the hatches, because the rising storm looks ominous.

This story was originally published on nationaljournal.com on December 21, 2017