Ever since GOP candidate Roy Moore lost a Senate election in Alabama, of all places, Republicans have been skittish. They are skittish about nominating a controversial, far-right candidate who turns off mainstream Republican voters, or, worse, who has skeletons in his closet that throw a winnable election. They are skittish about an energized Democratic base. They are skittish about what President Trump's unpopularity means for them.

And that skittishness has translated to another Deep South Senate race, this one in Mississippi, where all the things they fear could come to fruition. Sen. Thad Cochran (R) is resigning next month over health problems, leaving a rare open Senate seat up for grabs in November. Establishment Republicans fear they may again be stuck with yet another lackluster candidate, who could lose to a controversial challenger from the right — or that both of them are weak enough to lose to a Democrat.

Here's what's going on.

On Wednesday, Mississippi's governor appointed a relative unknown politico, state Agriculture and Commerce Commissioner Cindy Hyde-Smith, to hold Cochran's seat from April to at least November. Hyde-Smith is expected to run on Nov. 6 in a special election to keep the seat.

That election is a nonpartisan “jungle” primary, where candidates from all parties run. If no one gets more than 50 percent of the vote, there's a runoff three weeks later.

As The Post's Sean Sullivan and Josh Dawsey report, Republican leaders in Washington were underwhelmed with the governor's pick. Hyde-Smith was a Democrat until 2010. And she's untested in what is expected to be a tough intraparty battle, one that the GOP fears could put this Senate seat in danger.

“Alabama is fresh on everybody's mind,” one Mississippi GOP operative told The Fix.

To keep the seat, Hyde-Smith will have to defeat a challenger from the right wing of her party: Chris McDaniel. He's a well-known state senator and conservative radio host, known for calling Hispanic women “mamacitas,” among other controversial comments. McDaniel actually got more votes than Cochran did in the 2014 primary; he later lost in a runoff.

As The Post’s Robert Costa wrote during that 2014 race, McDaniel “has come to represent everything that establishment Republicans fear about the tea party: He is aggressive, unpredictable and, at times, insensitive — if not offensive — on matters of gender and race.”

And he has a loyal following. Trump endorsed McDaniel in his 2014 challenge to Cochran, calling him “strong” and “smart.”

But McDaniel hasn't exactly returned the favor. Like many Republicans — including Trump's new pick for secretary of state, Mike Pompeo — McDaniel dissed Trump during the presidential primary, saying he wasn't a “constitutional conservative.”

When McDaniel originally announced he was challenging Sen. Roger Wicker (R-Miss.) this November, Trump endorsed Wicker.

Still, if McDaniel wanted to paint himself as a Trump candidate, he probably could, especially since the White House isn't yet a fan of Hyde-Smith.

And that carries with it an eerily similar story line from Alabama, where Moore managed to win the GOP primary despite Trump endorsing the establishment pick, Luther Strange.

On the Democratic side, former congressman Mike Espy is running for the seat, and Democrats haven’t ruled out trying to recruit Attorney General Jim Hood, who has already proved he can win statewide as a Democrat, or Public Service Commissioner Brandon Presley.

Some Mississippi Republicans are comforted by a prevailing narrative that McDaniel's time has come and past. If he couldn't defeat Cochran in 2014, with the wind of the tea party at his back, what makes him think he can do it now?

Then there's this reality check even if McDaniel does win: Mississippi hasn’t elected a Democrat to the Senate in nearly three decades, and Trump won the state in 2016 by nearly 18 points.

But we said the same thing about Alabama.