President Trump didn't.
If Roy Moore had never run in the first place, Mo Brooks probably would have won the GOP primary in Alabama ... and would be a U.S. Senator from Alabama right now.
Mo Brooks called for Mitch McConnell’s ouster as Senate majority leader, and called him “head of the swamp”. That must have pissed off McConnell, who threw all of his support to Strange in the primary and then the runoff.
Trump’s endorsement of Strange was not a good decision on his part, but he was dependent on McConnell’s cooperation to move his agenda forward and as you say, Strange was a reliable vote. I’d say that was a “rock and a hard place” situation.
But to say that without Moore in the primary, Mo Brooks would have won is pure 20-20 hindsight speculation. Brooks couldn’t muster even 20% of the vote. Strange and Brooks would have split Moore’s vote, but it’s practically impossible to know with any certainty how that split would have gone.
We do know that McConnell threatened an ethics investigation if Moore had won. What would he have done if Brooks had been the nominee? Would he have withheld party support as he did with Moore? And if Brooks had won against Jones, what would he have done?
And what would the Rats have thrown against Strange if he was the nominee? You can be damn sure they would have made an issue of the slimy way in which he oozed into the Senate. What else would they have come up with? Bimbo eruptions? Financial misdeeds?
We will probably never know, but we can be pretty certain they would have come up with something damaging what with the power of the compromised FBI working hard to dig up dirt, and to invent dirt if necessary.
Would that, along with the ever-growing problem of vote fraud, have been enough to give Jones the victory over Strange? That seems unlikely, but again, that’s impossible to know.
But if the Republicans can’t come up with someone better than EITHER Moore or Strange, they deserve to lose.