Introducing his running mate on Saturday, Donald Trump stood alone behind a lectern bearing only his name and rambled for 28 minutes about his primary victories, what he called Hillary Clinton’s crimes against the country, how pastors should be allowed to endorse candidates and how he correctly predicted the outcome of the Brexit vote.

Occasionally, Trump mentioned his new “partner,” Indiana Gov. Mike Pence, mostly looking down to read from notes when he did. The presumptive Republican nominee insisted Pence was his “first choice” despite reports that he was uncomfortable with the decision until the end. Trump eventually invited Pence onstage, and the two shook hands.

“You’re amazing,” Pence whispered to him.

Then Trump left the stage. The interaction lasted all of six seconds.

The scene seemed as uncomfortable and forced as the pair’s original campaign logo — a massive “T” dominating a smaller “P” — and it underscored the uneasiness in this politically arranged alliance.

As Pence began speaking after Trump exited, he showed Republicans the role he will play in the campaign: the somber Midwestern conservative who sticks to the script and speaks reassuringly, if not rousingly, to the party’s conservative base. In carefully scripted remarks that lasted less than 12 minutes, Pence laid out a clear case for their partnership, something Trump had struggled to do earlier.

Pence also nodded toward the intrigue around his selection, telling the crowd that Trump called him on Wednesday to offer him the position. Trump had insisted as late as Thursday night that he had not made his “final, final decision.”

The event — held in a dimly lit ballroom at a massive Hilton hotel complex in Midtown Manhattan that was also hosting a weekend tattoo expo — was supposed to happen a day earlier, but Trump delayed it 24 hours because of the terrorist attack in Nice, France. It capped off perhaps the most ­chaotic and unconventional vice-presidential selection in memory, far different from four years ago when 2012 GOP nominee Mitt Romney introduced running mate Paul D. Ryan at a conventional rally in Norfolk with a massive crowd waving small American flags.

Instead, Trump took the stage as speakers blared “You Can’t Always Get What You Want” by the Rolling Stones — an odd choice given how much he wrestled with the choice. The crowd was small and included tourists off the street. Trump had the look of a candidate who had accepted that political calculation and unity mattered even for his unorthodox bid. He was a dutiful salesman, checking a box but not overwhelmed with enthusiasm about teaming up with someone with such a contrasting profile and personality.

Trump laid out reasons for picking Pence.

“If you look at one of the big reasons that I chose Mike — and, one of the reasons is party unity, I have to be honest,” Trump said. “So many people have said, ‘party unity.’ Because I’m an outsider. I don’t want to be an outsider.”

Later, Trump added, “So one of the primary reasons I chose Mike was I looked at Indiana, and I won Indiana big.”

As Trump began to list other reasons, he often stumbled off onto tangents: He gave a shout-out to his “many friends in Turkey, great people, amazing people” and wished them well in “resolving the difficulty” after an attempted military coup, then blamed Clinton, the prospective Democratic nominee, for leading President Obama “right down a horrible path” in the Middle East. He boasted of having won more votes in the primary than Ronald Reagan did decades ago when the population was smaller, and he gloated about defeating GOP delegates who tried to stop his candidacy. “They got crushed, and they got crushed immediately,” he said.

When Trump wrapped up these riffs, he occasionally transitioned back with a comment like “Back to Mike Pence!” This is when he would refer to the notes in his hands, as if he were unfamiliar with the topic.

Trump described Pence as “a solid, solid person” and “a man of honor, character and honesty” who helped Indiana’s economy, is not afraid to say the words “radical Islamic terrorism” and would help Trump fix the “rigged, rigged system” in Washington.”

Trump did not mention Indiana’s fight over religious liberty last year, which scared lesbian, gay, bisexual and transgender activists and delighted many evangelical voters. He denounced the North American Free Trade Agreement, calling it “the worst economic deal in the history of our country” without mentioning that Pence supported it.

As Trump reached the end, he could not help but bring up Pence’s endorsement of Sen. Ted Cruz (R-Tex.) in the primary.

“Governor Pence, under tremendous pressure from establishment people, endorsed somebody else — but it was more of an endorsement for me,” Trump said. “. . . It was the single greatest non-endorsement I’ve ever had in my life.”

Once Pence was onstage, the event felt like a traditional vice-presidential announcement.

A devout evangelical Christian and self-described “basic guy,” Pence called Trump a “good man, and he will make a great president of the United States of America” who understands the “frustrations and hopes” unlike any leader since Reagan.

It was subdued, low key and suggested a scene from a Norman Rockwell painting: of peaceful small towns and cornfields where God and family are paramount.

Pence’s flurry of shots at Clinton began soon after.

“We must bring a change to America’s standing in the world,” Pence said. “We can’t have four more years of apologizing to our enemies and abandoning our friends.”

As Pence finished, the crowd politely clapped and the running mate stood by himself at the lectern, seeming unsure of where to go. Soon Trump rejoined him, along with their families, waving and smiling as they all lined up together.

Afterward, Pence celebrated with his family over dinner at a Chili’s in New York. Then he traveled back to Indiana for a Saturday evening rally.

Trump did not join him.

Costa reported from Cleveland.