But Sen. Cory Booker, sitting in the passenger seat of Scholten's campaign Winnebago, had other ideas. Armed with his iPhone, Booker turned it on Scholten as the Iowa landscape flashed by.

"You are running for what?" Booker asked from behind his phone. Scholten responded, as he tried to keep one eye on the road, that he's running for Congress in Iowa's 4th Congressional District against Republican Rep. Steve King. Booker stopped him there.

"We only got 30 seconds a shot," the New Jersey Democrat said, tapping at his phone and publishing the first video to his Instagram story. Booker posts updates obsessively to his account, which boasts more than 400,000 followers.

This week, they were along for the ride with Booker on the campaign trail in Iowa, during day three of his first swing through the state as a buzzed-about potential 2020 presidential candidate. Officially, the visit was focused on boosting Democrats like Scholten ahead of the midterm elections. But Booker was also introducing himself to the influential party donors and activists who could make or break a presidential campaign in the key caucus state.

Other Democrats have also been jockeying for position in the party's invisible primary, in Iowa and elsewhere. Former Vice President Joe Biden has plans this week to visit South Carolina, another key primary state. Sen. Bernie Sanders will swing through Iowa later this month to campaign for Scholten and others. Sen. Elizabeth Warren has sent a fundraising appeal to her supporters on behalf of Cindy Axne, the Democrat challenging Rep. David Young in Iowa. And the list goes on and on.

Booker, 49, is no stranger to the Hawkeye State. He has Iowa roots, as he noted often during his visit: his maternal grandmother was born in Des Moines, and he still has family in the area - including his 99-year-old great-aunt Alma Morris, who was in the audience last Saturday. Booker's mother and a smattering of cousins and other relatives also cheered him on. The following day, the clan planned to gather for a reunion in Des Moines, away from the media glare.

Weeks in the making, Booker's big Iowa debut happened to coincide with the contentious Senate vote to confirm Judge Brett Kavanaugh to the Supreme Court. During the hearings, Booker had taken a star turn as one of the nominee's vocal opponents , garnering national attention for his "Spartacus moment" on the Judiciary Committee, including an appearance on "The Late Show" with Stephen Colbert.

Republicans also took notice, with Sen. John Cornyn chiding Booker during one hearing, "Running for president is no excuse for violating the rules of the Senate."

That didn't stop Booker from dashing straight from the Senate floor, where lawmakers narrowly voted to confirm Kavanaugh, onto a plane to Des Moines, a Mecca for so many presidential hopefuls. There, Booker headlined a major Iowa Democratic Party fundraising dinner, where he led a group therapy session of sorts for more than 1,000 donors and activists still reeling from Kavanaugh's confirmation.

"It was almost like the fellowship that I needed," Booker reflected a few days later in the RV. "The spirit, the energy of a whole bunch of folks that said, 'Regardless of what happened in Washington, we're not gonna curl up here, we're not gonna shut up here. We're not gonna give up here in Iowa.'"

On the road in Iowa

Booker was certainly not shutting up in Iowa. He seized the role of DJ during his brief road trip with Scholten, belting out each song at the top of his lungs. The playlist started with "Sioux City Sue," also the name of Scholten's RV; continued with "Born To Run," a nod to New Jersey; and then into "American Pie," inspired by the plane crash in Scholten's district that killed the famous musicians Buddy Holly, Ritchie Valens, and J.P. Richardson, known professionally as The Big Bopper.

"Everybody, the chorus! Come on, I can't hear you!" Booker hollered, swiveling his iPhone to capture his chief of staff, Matt Klapper, singing along sheepishly.

"Baby, we were born to run! Born to run, J.D.! All right, going down the highway in Iowa!"

In between songs, Booker continued his Instagram interview with Scholten. "Can we talk a little bit about the plight of farmers in Iowa?"

Booker's role as a popular surrogate for Hillary Clinton brought him to Iowa in 2016, where he made a strong impression among state Democrats. He recalled sitting in a diner with Clinton, speaking with the waitress, and being reminded of his home state.

"This might be the Midwest, I grew up in the Northeast," Booker said, "but folk are folk."

Booker has since continued to cultivate his network in the Hawkeye State. He spoke to the Iowa delegation breakfast at the 2016 Democratic National Convention, and his remarks "had members on their feet and literally roaring their approval," the Des Moines Register reported at the time. This election cycle, Booker has been endorsing candidates and, in a few cases, sending staffers to work on their campaigns.

And he has been beefing up his credentials on a key Iowa issue, agriculture - having toured farms in Missouri, Kansas and Nebraska in conjunction with a bill he is sponsoring to put a moratorium on big farm mergers.

Asked by a reporter how he, a New Jersey lawmaker, could understand rural issues, Booker said: "We have a great farm community. We are the Garden State. I don't know if I need to bring you a New Jersey tomato to let you know how good our produce is."

The sum of Booker's rhetoric and actions would suggest he is actively preparing for a presidential bid in 2020. In a recent interview with New York Magazine, Booker acknowledged that he's thinking about it. "Of course the presidency will be something I consider," he said. "It would be irresponsible not to."

Back on the RV, he wouldn't discuss his timeline for a decision, saying he plans "to spend all of my energy, all of my effort focusing on these next 30 days," during which time he'll be continuing to campaign for Democrats across the country.

"I'm going to Ohio, I'm going to Florida, I'll be going to a whole bunch of other states, I'm going up and down Jersey again for (Sen.) Bob Menendez," Booker said. "And that's where 100% of my focus is. We can talk about 2019 and 2020 after this."

Trump zeroes in on Booker

President Donald Trump, for one, isn't waiting to talk about it, having zeroed in on Booker as one of the Democrats possibly standing between him and reelection to a second term.

"Take a look at Cory Booker," Trump said during an event at the White House last week. "He ran Newark, New Jersey, into the ground. He was a horrible mayor. And he made statements that when he was in high school or college, what he was doing - he actually made the statements. And now he's talking about Judge Kavanaugh."

Booker responded this week by attempting not to respond, saying he has "nothing personal against this President."

"If he wants to attack me personally, he can," Booker said. "If he wants to attack my record, the reality is that the people of the state of New Jersey who elected me statewide are very proud of the work that I did, the change that we made in Newark, the transformation going on in our city."

"This is not about the President, this is not about me," Booker went on. "I will never let him pull me so low as to hate him. I'm going to continue to be a voice in this country for love, for bringing the nation together, not driving the nation apart."

It's unclear whether such a message of "love" will resonate with Democrats in the time of Trump, with many activists urging the party to fight the President's fire with fire. The attorney Michael Avenatti has been among those advocating a more aggressive tack, saying at a recent Vanity Fair event that if Democrats "have to crawl in the gutter with this person, then that's what we have to do."

"You're not going to beat Donald Trump with a message of universal love," said Avenatti. "This guy will eat you alive."

But Booker disagrees.

"Look, I'm angry, I'm hurt. I'm upset about what's going on and how real people in America, working folks are being treated," Booker said. "But the way you counter that is not by embodying the tactics of those people that you don't want to see in office. So, the President might try to divide people, I think we as Democrats should try to unite people."

"And so I don't know if it's a winning political message or not," he added, "but I will always be talking about trying to unify this country, trying to bring us together."