Vice President Pence's lukewarm endorsement of Sen. Ted Cruz during last year's critical Indiana Republican presidential primary played a key role in President Trump's decision to reach out to Pence as a potential running mate.

The key role of the Cruz endorsement — during which Pence spent a significant amount of time praising Trump — is documented in a newly released batch of emails from Pence's time as governor.

Local political blogger Abdul Hakim-Shabazz speculated in early July 2016 that the Trump campaign reached out to Pence in large part because of the Cruz endorsement. Pence's then-Chief of Staff Jim Atterholt sent his boss a copy of the article.

"I really like his narrative as it happens to be true," Atterholt wrote to Pence's personal AOL email account on July 3, 2016.

The email was obtained by IndyStar through a public records request.

In an interview Thursday, Atterholt confirmed that Pence's handling of the Cruz endorsement got Trump's attention and sealed the deal for a meeting with Pence at Trump National Golf Club in New Jersey to discuss the vice president post.

"It played a significant role in building the relationship between Pence and Trump, which led to Trump later reaching out to discuss the vice presidential position. No question it was significant," said Atterholt, now chairman of the Indiana Utility Regulatory Commission.

While other factors weighed heavily in Trump's decision, including Pence's standing among social conservatives and his familiarity with Congress, the Cruz endorsement played a particularly important role, Atterholt said.

"I don’t want to comment on conversations I had with Mike Pence," he added. "But I know this to be true. I have direct knowledge that this is indeed true."

Pence threw his support behind Cruz on April 28, just days before Indiana's primary. Despite the endorsement, Trump won the race, prompting Cruz to drop out of the race and cementing Trump's status as the GOP presidential nominee.

During the endorsement on a conservative Indianapolis talk radio program, Pence said he would vote for Cruz but stopped short of calling on others to vote for the Texas senator.

He also heaped praise on Trump, who he said "has given voice to the frustration of millions of working Americans with a lack of progress in Washington D.C."

"And I'm also particularly grateful that Donald Trump has taken a strong stance for Hoosier jobs,” Pence said.

During the final days of the Indiana campaign, Trump frequently highlighted the lukewarm nature of Pence's endorsement of Cruz, calling it "a very weak one” and suggesting Pence’s decision came after “a lot of pressure from his donors.”

"I think what he said about me was nicer than what he said about Cruz,” Trump saidduring one of his final Indiana campaign stops.

Although Pence's endorsement was widely panned as "tepid" and "lukewarm," Atterholt said it ultimately played a key role in the Indiana's governor's rise to the nation's second highest office.

"It was a significant piece in that very intricate puzzle," Atterholt said. "The way then-Gov. Pence handled the Trump portion of the endorsement really surprised then-candidate Trump. It had a significant impact on him. I think Trump was used to New York-style politics where you bash the person you’re not endorsing."

Pence declined to comment for this story through his spokesman, Marc Lotter.

“We’re not going to comment on what the thoughts of the then candidate were,” Lotter said. “Jim confirmed that’s what he said in the email. Jim expressed his thoughts on that. I would just leave it with that.”

IndyStar also reached out to the White House for comment from Trump, but has not received one.

The emails were provided to IndyStar in response to a public records request originally filed six months ago. The office of Gov. Eric Holcomb, Pence's Republican successor, said it is withholding an undisclosed number of emails because they are deliberative or confidential.

Holcomb's office said additional emails would be forthcoming.