WASHINGTON >> Newt Gingrich and Donald Trump peer into the camera phone lens with all of their grandfatherly chins and smile lines. Look, Gingrich says quietly, we’re on Facebook, live and worldwide. Trump, a master of Twitter, marvels.

“It’s the modern world,” Gingrich, 73, says.

“It’s the modern world,” Trump, 70, agrees.

So far so good. The backstage selfie video was part of Gingrich’s campaign for a role he’s never played in four decades of public life. Whether he is named Trump’s running mate or serves otherwise as the Republican presidential candidate’s adviser, Gingrich has become an understudy to a because-I-said-so billionaire who is given neither to partnerships nor the intricacies of public policy.

Onstage a few minutes later, Gingrich fired up Trump’s supporters by predicting the billionaire would “kick over the table” in Washington. The enthusiasm Gingrich generated lingered into Trump’s rambling speech, interrupted several times by shouts of “Newt! Newt! Newt!”

Running mate or not, “Newt Gingrich is going to be involved with our government,” Trump said.

But not as principal table-kicker of old, who toppled 40 years of Democratic control in the 1994 “Republican revolution” and became House speaker in the tumultuous years of Bill Clinton’s presidency. Should Trump win, it will be president shaking things up.

Thursday evening’s rally in Cincinnati raises questions: How would a former history professor, former No. 2 in the presidential line of succession and a man known as “Nuclear Newt” in his 2012 presidential campaign play second banana to Trump? And why would Trump, his own favorite adviser, bring aboard such a restive figure?

The answers, according to Gingrich’s longtime colleague and friends, lie in the skills and political advice the former Georgia congressman could lend to the billionaire.

“Newt used to take himself so seriously, but I think that is gone now,” said Katon Dawson, who worked for Gingrich and helped him win South Carolina in the 2012 GOP primaries. “I think Newt realizes now that he’s not going to be president of the United States. But he’s got a chance of being vice president of the United States. And he’s ready to play the game.”

Bob McAlister, who helped run Gingrich’s 2012 campaign in South Carolina, sees a sweet spot where the two lifelong alphas could make a powerful pair: Where Trump needs political sophistication or policy details, Gingrich can help. Trump could be “the big-picture guy.” That might require both men to share the campaign control stick in a way that steers the whole enterprise away from drama and toward victory.

“Somebody would have to give some,” McAlister said. “It is obvious to me that Trump, A) does not want to be the detail person and, B), probably can’t do it if he wanted to. So Trump’s weaknesses would be strengths with Newt onboard — if Trump would allow it.”

The political environment, hostile to government insiders and the American elite, favors both men in that way. Trump is seen as standing up to people in power much like Gingrich was in his 2012 campaign.

Gingrich could help elect vulnerable Republican House and Senate candidates who are hesitant about aligning with Trump. Should a Trump-Gingrich ticket win, Gingrich could squire Trump around Washington and smooth feathers where Trump ruffles them, as he did last week during what was supposed to be a unity luncheon with senators.

The professorial Gingrich, says Dawson, could teach Trump from personal experience how to toughen his thin skin to Washington standards.

“He still has enough ego for the body armor that all politicians require,” Dawson said of Gingrich.

Not all Trump advisers are on-board with the idea of Gingrich as running mate.

Among their concerns: Gingrich’s three marriages included public admissions of infidelity, which irks some social conservatives. And Gingrich remains in debt from his unsuccessful 2012 presidential bid. The campaign owed vendors almost $5 million as of April, according to Federal Election Commission reports. Among those owed: pollster Kellyanne Conway’s company. She’s now working for the Trump campaign.

Some in Trump’s circle fear that deploying Gingrich against Hillary Clinton would ignite a backward-looking replay of 1990s dramas, when Gingrich pushed for Bill Clinton’s impeachment.

And that could renew attention on unflattering episodes of Gingrich’s Clinton-era history, including a budget standoff that ended in a government shutdown, a near-mutiny by Gingrich’s own House allies and an ethics tangle for which Gingrich paid $300,000 toward the cost of the inquiry.

That backstage Facebook lesson? It was a lesson for Gingrich, too — that the job would mean following orders.

“I finally got something like 90 seconds out of him,” Gingrich told The Washington Post. “Then he started to say, ‘We’ve got to get out there, we’ve got to get out there!’ So I said, ‘OK, I’m heading out there.’”