Donald Trump once boasted his followers love him so much they’d stick with him even if he shot somebody on the street. Fortunately, the 45th president has yet to test that theory.

But Trump did ignore a wise bipartisan, political practice that presidents let party primaries play out before getting involved with endorsing anyone.

Reportedly at the urging of Senate Majority Leader Mitch McConnell, the president jumped into Tuesday’s Alabama GOP Senate runoff  anyway and endorsed incumbent Sen. Luther Strange. So did Vice President Mike Pence. Both men also campaigned for Strange.

Trump’s supporters left the president out on the street, embarrassed and alone. Strange’s opponent, Roy Moore, a rogue conservative, won handily, 55% to 45%. Also tossed on the street was McConnell whose allies invested — or wasted — millions trying to drag the lackluster, appointee Strange back to Washington.

Now come January, McConnell won’t have just an unpredictable president of his own party to deal with. He’ll also have to contend with and answer for an unpredictable firebrand senator who’s given to less than eloquent comments on race, same-sex marriage and the like. And someone who roundly denounced McConnell throughout the campaign.

That is if — and it’s now a LARGER if — Moore wins in the actual special election against Democrat Doug Jones, who says he’s pro-life after birth. He’s an ex-federal prosecutor, who says Alabamans are tired of distractions from pocketbook issues and being embarrassed by their politicians.

The last time the Heart of Dixie sent a Democrat to the U.S. Senate was Howell Heflin in 1990. He was succeeded by Jeff Sessions, another former federal prosecutor whose resignation to become Trump’s Attorney General last winter started all this appointment and special election mess.

These developments are further evidence of GOP disunity on Capitol Hill (and beyond) and a profound dissatisfaction within the base over the lack of congressional legislative successes now that, as routinely requested, voters delivered a Republican president to sign all the conservative measures that two Republican-controlled chambers were going to be sending to the Oval Office.

There was, for instance, the long-promised repeal of ObamaCare. Oh, wait. That failed several times — and at the hands of fellow Republicans themselves. Still no tax reform or major infrastructure package.

On top of all that on the same election day, incumbent GOP Sen. Bob Corker, faced with a certain primary challenge in Tennessee next year, gave up after two terms and announced his retirement then.

Given the clear grassroots party ferment and the willingness of irregulars like Steve Bannon to challenge establishment party types, more retirements are expected before the holidays. Each open seat, well, opens another opportunity for Democrats.

For other possible departures, can you say Orrin Hatch, Susan Collins, Thad Cochran, Jim Imhofe and, for health reasons, possibly John McCain, among others? That’s a lot of institutional memory, seniority and potential replacement elections to lose.

Even if they slog on, incumbents like Arizona’s Jeff Flake and Nevada’s Dean Heller face costly and often politically bloody primary challenges.

In a classic bit of dubious bet-hedging, during an Alabama rally last week President Trump said of his friend Sen. Strange:

If his opponent (Roy Moore) wins, I’m going to be here campaigning like hell for him. Roy has a very good chance of not winning in the general election.

But after the outcome, the president’s Twitter account graciously sent good wishes to victor Moore:

Congratulations to Roy Moore on his Republican Primary win in Alabama. Luther Strange started way back & ran a good race. Roy, WIN in Nov!

Roy can not do that, however. The special election is in December.