It’s hard to ignore the storm clouds gathering for Republicans looking toward the 2018 elections. Midterms are typically referenda on the incumbent president and the party in power, and Donald Trump’s job-approval ratings are lower than those for any newly elected president. Worse still, a badly divided Republican Party holds precarious margins in both the House and Senate and so far has a meager record of legislative accomplishments.

Most congressional-race analysts see the fight for control of the House to be very tight, with the winner likely holding a razor-thin margin. A single-digit-seat majority for one side or the other is a very real possibility. The bad political environment for Republicans may be mitigated, at least in part, by congressional maps and natural population patterns that work against Democrats.

But what about the Senate? Is the Republican 52-48 majority in as much danger as its margin in the House? Arithmetic would suggest that a 52-48 advantage is more precarious than a 55 to 45 percent Republican edge in the House, but is that really the case?

I would argue that Republican odds of hanging onto the Senate majority are pretty good—in fact, amazingly good given the political environment. Indeed, it is difficult to see how Democrats secure the three-seat net gain necessary to win a majority. Regular readers of this column know the numbers by heart: five Democratic incumbents up in states that Trump won last year by 19 points or more, five more Democrats up in states that Trump won by single digits, and only one Republican, Dean Heller in Nevada, up in a state carried by Hillary Clinton.

Think step by step exactly what Democrats need to do to get a net gain of three seats. First, they would have to hold all of their 25 seats in play next year, a tall order given how many Democrats are running in enemy territory. Some Democratic senators have been riding a wave of political luck. They were elected in 2006, the second midterm elections under President George W. Bush, whose popularity had been battered by the Iraq War. The next time this class was up, in 2012, Mitt Romney was an asset in very few states. President Obama won by a wider margin than expected, creating a favorable climate for Democrats as well.

The second requirement for a Democratic Senate majority would be beating Heller in Nevada. He’s no pushover. He was elected in 2012, on the same day that Obama was beating Romney in the state by almost 7 percentage points. Heller’s margin was just over one percentage point, but when you run roughly 8 points ahead of the top of your ticket, you are doing pretty well.

The third step for Democrats would be to beat Sen. Jeff Flake, keeping in mind that the last time a Democrat won a U.S. Senate race in Arizona was the reelection of Dennis DeConcini in 1988, 29 years ago.

But if steps one through three are really hard, step four is much more difficult. One implausible path would require Democrats to win the special general election this December in Alabama, which last elected a Democratic senator in 1992 (Richard Shelby, before he switched parties in 1994).

The political jockeying in Alabama began when Luther Strange, then the state’s attorney general, was appointed to fill the Senate seat vacated by Jeff Sessions when he became attorney general. Strange is a conventional, pro-business Republican who generally tries to tread lightly on social and cultural issues. He fits right in with Mitch McConnell, John Cornyn, John Barrasso, Roy Blunt, Lamar Alexander, and others who make up the GOP Senate establishment. By contrast, his Republican opponent, the flamboyant former state Supreme Court Justice Roy Moore, would be inclined to roll ideological grenades down the center aisle of the Senate chamber.

The victor in that runoff will be up against the squeaky clean former U.S. Attorney Doug Jones, a white prosecutor who reopened a cold case, the 1963 bombing of Birmingham’s 16th Street Baptist Church, in which four young African-American women were killed. It was considered a major coup when Jones secured convictions of two former members of the Ku Klux Klan.

There are signs that Trump might be reconsidering his embrace of Strange, but no one really knows what the president might do. Trump’s base is more aligned with Moore’s voters, while the GOP establishment is strongly in the Strange camp.

The alternative Democratic path would require beating Ted Cruz in Texas, a state that last elected a Democratic senator in 1988, when Lloyd Bentsen was simultaneously reelected while standing as Michael Dukakis’s running mate.

So is there a weak spot in the Republican firewall? If Heller, Flake, or some other GOP incumbent either loses in the primary or becomes so badly damaged that he is unelectable, then the Democrats have an opening. Both Heller and Flake face vigorous primary opposition from the Right. One thing to watch in each race is whether the anti-incumbent vote rallies behind a single challenger or fragments behind several, tipping the advantage back to the incumbent.

While there are other theoretical ways for Democrats to score a net gain of three seats, they face long odds because only 10 GOP seats are in play. A lousy political environment is not nearly enough to cost Republicans the Senate majority. If the Republicans go down, it will require self-inflicted wounds.

This story was originally published on nationaljournal.com on September 8, 2017