President Trump spoke on a variety of topics at a Sept. 22 rally in Huntsville, Ala., where he was campaigning for Sen. Luther Strange. (The Washington Post)

HUNTSVILLE, Ala. — President Trump campaigned on Friday night for Alabama Senate candidate Luther Strange, in a race that has pitted him against his most loyal supporters and that holds the potential to upend the political dynamics for Republicans facing election in 2018.

The endorsement of ‘Big Luther’ could prove to be a big boost for the interim Alabama senator, who is trailing his opponent, former state judge Roy Moore, in some public polls. But even Trump seemed unsure that the endorsement was the right move.

“I’ll be honest, I might have made a mistake,” Trump told the crowd at one point during his nearly 90 minutes of remarks.

“If Luther doesn’t win they’re not going to say, we picked up 25 points in a short period of time,” he added, referring to the media. “If his opponent wins, I’m going to be here campaigning like hell for him.”

After some musing, he seemed to catch himself.

“Luther will definitely win,” Trump said.

It may not have been exactly the ringing endorsement Strange’s campaign had hoped for, but it would have to do.

Trump is jumping into the special election at a time when Strange could use all the help he can get before the primary election on Tuesday night. The Alabama Republican is favored by establishment Republicans including Senate Majority Leader Mitch McConnell (R-Ky.), but has been pilloried by Moore, who has fashioned himself as an outsider Republican in the mold of Trump himself.

For his part, Strange has draped himself in Trump in an effort to win over the president’s ardent supporters. So much so that the Friday night rally bore few signs that its purpose was to boost his candidacy.

Everything about the rally — the mega stadium, the massive American flag, the “Make America Great Again” hats — screamed Trump. There were few signs that the rally was for anyone else, except for the giant Trump campaign-styled “Vote for Luther” sign that hung in the background.

The president delivered a signature rally speech, meandering from topic to topic, prompting laughter, and chants of “Lock her up!” from the crowd when he mentioned his former Democratic opponent, Hillary Clinton. He denounced the “dishonest media” who he said would not broadcast images of the crowd (though they often do). And he complained about the treatment of first lady Melania Trump in the media.

Then, without much warning, Trump returned to his prepared remarks touting Strange.

“Luther wants to end business as usual, stop the insider dealing and Luther Strange is determined to drain that swamp,” Trump said, in a brief interlude.

Trump talked at length about Strange’s willingness to vote in favor of the Republicans’ bill to repeal the Affordable Care Act without seeking any favors in return. He said his endorsement of Strange came despite his unwillingness to wade into an ongoing primary.

“We have to be loyal in life,” Trump said. “He never went quid pro quo, he just treated me great.

“And I’m calling him. He was down like quite a bit and I said I’m going to endorse you,” Trump continued. “I shouldn’t be doing it … The last thing I want to do is be involved in a primary.”

But Strange had given him one of the “coolest” moments of the last six months of his life, Trump told the crowd. So he came to Alabama to get out the vote for Strange in the final days of the primary campaign.

But, quickly, Trump was back to his usual campaign fare.

He boasted of his electoral college win.

“They said there was no path to 270 but there was a path to 306,” Trump said.

He admonished Clinton for failing to travel to Wisconsin during the campaign and dismissed the idea that Russia interfered in the election to help him.

“In case you were curious, no, Russia did not help me,” Trump declared.

He returned again to Strange, who apparently watched the rally from somewhere offstage.

Both men were on message on one important point: The Senate majority leader was persona non grata.

“He’s not a friend of Mitch McConnell, he doesn’t know Mitch McConnell until recently,” Trump said, decrying the “bad rap” that Strange’s opponents had saddled him with as an establishment candidate. “He doesn’t know him, he just got there!”

Moore, a controversial former state judge, boasts the support of prominent pro-Trump figures, including two ex-White House staffers, chief strategist Stephen K. Bannon and his terrorism aide, Sebastian Gorka.

At a rally in Montgomery on Thursday night, former Republican vice presidential nominee Sarah Palin pitched the race, and Moore’s candidacy, as a fight for the soul of Trumpism.

“A vote for Judge Moore isn’t a vote against the president,” Palin said. “It is a vote for the people’s agenda that elected the president. It’s for the big, beautiful movement that we’re all a part of. The president needs support to keep the promises that elected him. So we’re sending Trump someone who has our back, not Mitch McConnell’s … Make no mistake, ‘Big Luther’ is Mitch McConnell’s guy.”

The dissent among Trump allies even came from within his own Cabinet.

Housing and Urban development Secretary Ben Carson issued a statement on Friday backing Moore’s candidacy, an extraordinary endorsement that came just hours before Trump was set to arrive in Alabama to campaign for Strange.

“Judge Moore is a fine man of proven character and integrity, who I have come to respect over the years,” Carson said. “He is truly someone who reflects the Judeo-Christian values that were so important to the establishment of our country.”

Recent polling in the state shows Strange trailing Moore despite the political muscle backing him.

Republicans worry that if Strange falls to Moore, the race could launch a tsunami of outsider challenges to incumbent Republican lawmakers in the next midterm election.

Trump warned the crowd that Moore would be vulnerable to losing to the Democratic candidate in the general election while Strange would sail through to victory.

“Roy has a very good chance of not winning in the general election,” Trump said. “Roy is going to have a hard time, but I will be backing him if he wins.”

And he lamented that Strange, who he noted had fought against public corruption in his previous career as attorney general of Alabama, had been saddled as an establishment candidate. Strange was appointed by the Alabama governor to fill the seat vacated by former senator Jeff Sessions, who has become the U.S. attorney general in the Trump administration.

“Friends of mine have told me very strongly that if Luther wasn’t appointed in office … he’d be leading every poll by 50 points,” Trump said. “But the fact that he got appointed hurt him.

“If Luther didn’t take an appointment, if he just ran, it wouldn’t be a contest,” Trump said.

As Trump faces the prospect that his chosen candidate might not emerge the victor, he has fixated on what his endorsement has done to help Strange catch up in the polls.

“If Luther doesn’t make it, they’re going to go after me,” Trump said, referring to the media. “He went to third, second and now it’s almost pretty even right?”