The sight of a Democrat, Doug Jones, being sworn in as the new US Senator from Alabama must have been a wrenching experience for Senate Majority Leader Mitch McConnell to watch. Despite offering the customary congratulations to Jones for becoming the club’s newest member, McConnell and his Senate Republican colleagues were probably grimacing with pain on the inside. No Republican with a pulse should have lost the special Senate election in Alabama, a state as red as the steaks that GOP bigwigs have when they commiserate over how best to enact President Trump’s agenda.

But there it was, a Democrat plopping down in a seat a Republican should be sitting in.

Before Congress adjourned for the holiday break, McConnell didn’t mince his words as who should be blamed for the upset: former White House chief political strategist Steve Bannon. “Well, let me just say this,” McConnell told reporters during his end of the year news conference, “the political genius on display of throwing away a seat in the reddest state in America is hard to ignore.”

Even with unified Republican government in Washington, 2017 was an unpredictable, roller-coaster year for the veteran Washington insider. The implosion of GOP nominee Roy Moore was just one more kick in the shin for the majority leader—a man used to doing battle with Democrats on legislation, not fellow Republicans during a campaign. 2018, however, could be an even bigger migraine for McConnell and the his Senate Republican conference.

A slim majority

Thanks to Doug Jones victory in Alabama—the first time a Democrat won a Senate seat in the state since 1992—McConnell is left with a one-seat majority with very little if any room to spare on major legislation. Even the majority vote reconciliation tool Republicans used to pass the tax bill this month may not be enough to get a GOP priority through the upper chamber. McConnell has a handful of independent-minded senators who aren’t afraid of bucking the conference depending on the issue (Rand Paul on the debt, Bob Corker on the deficit, John McCain on defense and healthcare, and Susan Collins, Lisa Murkowski on healthcare), and it will only take two of those people to essentially hold the entire GOP conference hostage. McConnell will need all of the whip-cracking skills he has learned during his career to keep his fragile coalition together.

A bad political climate

2018 is a midterm election year, which means Republican lawmakers will be debating and voting on every major issue with electoral politics in the front of their minds. And the politics for Republicans, at least at the present time, are not promising.

Based on polling data from NBC News and the Wall Street Journal, Americans would rather have Democrats control Congress than Republicans by an 11-point margin (50%-39%). The last time Democrats had such high numbers on this question was in Sept. 2008, less than two months before Barack Obama would waltz into the White House and Democrats would expand their majorities in both houses. Republican voters are also growing more negative about the party; 39% of Republican or Republican-leaning voters surveyed by the Pew Research Center said they were somewhat or very pessimistic about the GOP’s future.

Outside the numbers, the Trump presidency has energized Democrats throughout the country. More Democratic candidates are exploring political office and more women than ever before are thinking about launching campaigns. While the GOP is raising a lot of money, you don’t see the same level of excitement. Whereas aspiring Democrats are preparing to run for Congress, moderate Republican incumbents are choosing to retire.

Trump will be Trump

McConnell and Trump may have a cooperative working relationship now, but the two men are polar opposite personalities with different experiences and temperaments. And they’ve had their share of brush-ups.

When the Senate failed to overhaul Obamacare in August, Trump pinned the defeat on McConnell’s shoulders and publicly scorned him. He went on Twitter and typed up his bewilderment about why the majority leader “couldn’t get it done.” He slyly suggested to reporters at the White House that the senior senator from Kentucky should give up his post if he couldn’t get his agenda passed. McConnell didn’t take too kindly to the criticism, griping in private that Trump didn’t understand the basics of governing, and whose bull in a china shop routine is so out of control that it was beginning to hurt the party’s image.

Republicans are going through a kumbaya moment right now after the tax bill victory, but how long will the celebration last? It’s not hard to see Trump reverting back to his previous behavior. If he doesn’t blame Chuck Schumer and Nancy Pelosi, Trump will likely bash McConnell if an infrastructure bill doesn’t pass, or if Congress doesn’t appropriate the money needed to finance his supposed Ronald Reagan-style defense buildup.

Senator Romney?

Orrin Hatch’s decision to retire after 42 years in the Senate provides Mitt Romney, the former Massachusetts Governor and 2012 Republican presidential nominee, with a political comeback on a silver platter. Romney is an enormously popular figure in Utah, has deep roots in the state’s Mormon community, knows the movers and shakers in Utah politics, and would likely run away with the seat if he were to run as Hatch’s replacement.

Why would a prospective Sen. Romney be a problem for McConnell? On legislation and policy, the answer is he wouldn’t be. But when you throw Trump into the formula, Romney’s presence in the Senate will likely help contribute to a Republican Party that is already polarized between Trump diehards, committed Never Trumpers, and conservatives in the middle whom Trump too often brands as insufficiently loyal to his America First agenda. It goes without saying that Romney is the model Never Trumper, the man who humiliated Trump during a nationally-broadcast campaign speech as a “phony” and a “fraud” who didn’t have the mental stamina and emotional stability to be president. It’s one of the reasons Trump lobbied Hatch to run again in 2018—the last thing the White House wants is another conventional Republican.

This puts McConnell in an awkward position. He has a responsibility to defend members of his caucus and boost the electoral fortunes of establishment Republican candidates. But if McConnell is seen as too deferential to a Romney candidacy, he could once again be the victim of Trump’s wrath.

Bannon isn’t going away

Roy Moore’s defeat to a Democrat in Alabama notwithstanding, former White House chief political strategist and populist provocateur Steve Bannon is not at all deterred from making McConnell’s life miserable. He’s been the focus of two magazine profiles (in Vanity Fair and Newsweek) in December, has a mouthpiece at SiriusXM satellite radio, the full Breitbart website at his disposal, and a relationship with the wealthy Mercer family. His juicy comments in Michael Wolff’s new book have lit up the internet. But just as important as all those resources, Bannon has an extreme determination to unseat McConnell as majority leader.

Bannon-backed candidates in Arizona, Nevada, New York’s Staten Island, Montana, and Wyoming are preparing to primary establishment Republican incumbents this year, forcing McConnell-aligned Super PAC’s to spend money that would normally be saved for the general election contests. It is not beyond the scope of the imagination for Trump to even endorse some of these primary challengers, sowing yet more turbulence within GOP waters.

Mitch McConnell knows the ways of Washington like the back of his hand, having operated in the corridors of power for decades. But this year may be unlike any other he’s lived through, a period that could be even more chaotic, disappointing, and bittersweet than the opening act of Trump’s presidency.