Remember, there are three candidates jockeying for position. First is Rep. Martha McSally, the fighter pilot turned congresswoman who’s the establishment pick for the nomination. There’s Kelli Ward, the populist backed by Steve Bannon who was cruising towards a primary upset of Jeff Flake until Flake retired, opening the door for McSally. And there’s latecomer Sheriff Joe Arpaio, the hyper-populist border hawk who’s seeking his first Senate term at age 85. Typically there are two lanes in a contested Republican primary, the moderate and the populist, but Arpaio’s surprising decision to jump in and get to Ward’s right means she’s momentarily left without a lane. Her best play may be to ride the dividing line, positioning herself as less establishment than McSally but less fringey/more electable than Arpaio. Not too hot, not too cold. Just right.

Unless, that is, she’s able to land POTUS’s endorsement. In a field divided three ways, Trump’s support might be decisive. He could certainly play kingmaker between Ward and Arpaio by supporting one of them over the other. His favored candidate would probably quickly consolidate populist support, all but ending the other populist candidate’s hopes. And with only one populist in the field instead of two, McSally would suddenly be in a lot of trouble. She can win a three-way race if Ward and Arpaio split the right-wing vote, but if the right isn’t split, and if Trump has jumped in to support its preferred candidate, McSally may be sunk. All that’s standing between the GOP and Joe Arpaio, Senate nominee, is Trump holding off on an endorsement.

If you believe the Times’s sources, he might indeed hold off. Indefinitely.

Ms. McSally has been helped by an aggressive backstage effort from Republican officials in and out of the White House to keep the president from backing Mr. Arpaio or Ms. Ward. Before she entered the race, Ms. McSally won assurances from an intermediary that Mr. Trump would not endorse her rivals, according to a Republican directly familiar with the conversation, and she and her advisers met last week in the White House with the president’s political team, an opportunity not afforded the other candidates.

To further inoculate herself from the right, Ms. McSally is declining to say whether she would support a comprehensive measure that offers legal status to undocumented immigrants and is publicly showering Mr. Trump with praise, though she will not reveal whom she voted for in 2016 or any election.

Imagine how different things might be if 12,000 voters who backed Doug Jones in the Alabama special election had supported Roy Moore instead. If Moore had won, even though he would have *vastly* underperformed a generic Republican in that state by eking out a narrow victory, Trump might have concluded that Bannon had been right all along. “His people,” the Republican base, wanted populist nominees and were prepared to turn out in the general election to lift them to victory. Instead Moore blew a lay-up, handing Trump his second embarrassing rebuke in a red state in the span of several months. Trump had endorsed Luther Strange in the primary runoff because the GOP establishment assured him that Strange stood a better chance of winning the seat than Moore. (Which was true.) But Republican primary voters didn’t care. So when Moore won the runoff, Trump swung behind him and continued to stand behind him as ugly stories of Moore’s alleged interest in teenaged girls started to bubble up. And then Trump lost that bet too.

The obvious play in Arizona, then, would be not to endorse anyone in the primary while quietly working with McSally’s team behind the scenes to try to help her to the nomination. It sounds like that’s exactly what POTUS is doing. He doesn’t want to endorse McSally or else the Bannonites in his base will be miffed but he doesn’t want to endorse Ward or Arpaio either for fear of a Moore replay in the general election. Keeping his powder dry is the prudent move. Just one question: What happens if Ward or Arpaio drops out of the race, either because they’ve concluded for whatever reason that they can’t win or because John McCain is forced to resign for health reasons and Ward or Arpaio decides they’d rather run for the vacancy for his seat instead? That would leave McSally head to head with a single populist candidate, her nightmare scenario. Potentially the only thing that’ll save her in that case is … a presidential endorsement. After the Luther Strange debacle, does Trump want to risk having his base reject his preferred candidate again?

One other obvious what-if: What if Steve Bannon hadn’t been so stupid as to badmouth Trump Jr to Michael Wolff? Would that have made Trump more likely to back Arpaio or Ward? The Trump/Bannon feud of the past six weeks has proven conclusively which of them the populist right is loyal to, to the point where Bannon had to leave his “killing machine” at Breitbart, but that doesn’t mean Bannon lacked influence in shaping right-wing opinion. It was his candidate in the Alabama primary, not Trump’s, who won the Republican runoff. With Bannon at the helm of Breitbart, Trump might have suffered some injuries from populist media if he eventually backed McSally over Ward and Arpaio in Arizona. With Bannon in Siberia, though, who’s going to rap his knuckles if he goes with the establishmentarian this time? After the Alabama debacle, who would even fault him for supporting the most electable Republican in the race given how tight the GOP’s margin in the Senate is likely to be next year?

Take three minutes and read the entire NYT piece on Arizona, which is filled with amusing tidbits in which McSally strains not to criticize Trump despite her obvious lukewarm feelings about him. There’s also a helpful aside in which the widely disliked Jeff Flake says he cringes when he sees her buddying up to POTUS, to which McSally replies, “I’m not seeking his political advice.” Getting into a war of words with her is one of the most useful things Flake could do to help polish her own populist credentials a bit. I wonder if his criticism was deliberate, with that strategy in mind. In lieu of an exit question, here’s another amusing tidbit from CNN this morning — not about McSally and Trump but about Bannon and Trump.