Former Secretary of State Hillary Clinton, accompanied by her husband former President Bill Clinton, speaks at a campaign event in Davenport, Iowa January 29, 2016. (Melina Mara/The Washington Post)

In a rural roadside restaurant here in the heart of Puerto Rico, the lunch rush was over, leaving only a handful of patrons to see a snowy-haired figure in black jeans and a polo shirt emerge from an SUV that pulled up outside.

It was the 42nd president of the United States. Within minutes, just about everyone in the place had pulled out a smartphone for a photo with Bill Clinton. He lingered a bit with a group at the bar, accepting a cold bottle of Medalla, and toasting with them: “To Hillary!”

“Good beer,” he declared.

That was one of the six stops that Clinton made last Tuesday, as he scouted for votes from the northern coast of the island to the southern one. His day also included three rallies, lunch with local political leaders at a San Juan restaurant and a tour of a distillery, where he sipped ­27-year-old rum tapped straight from a barrel.

Bill Clinton’s schedule many days is more packed than Hillary’s, though by design it rarely registers on the national radar.

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This is the invisi-Bill campaign. The former president who flickers occasionally on cable news channels remains a big draw on the off-Broadway circuit of presidential politics. It is a low-altitude tactical deployment that leaves a light footprint, aiming to maximize his value as a political asset without stirring the negatives that also trail him.

His new duties have not come without stumbles, and they conjure the implications of a Clinton restoration. Presidential spouses are expected to exert their influence over china patterns, not China policy. No one, however, is under the illusion that Bill Clinton would remain cloistered in the East Wing. Still open to question is whether voters will welcome his return or worry about it.

Clinton has not sat for a formal media interview since last fall. But he pops up in obscure and unlikely places, where the presence of the former president is certain to dominate local front pages and evening newscasts and generate buzz in the community.

Usually, he draws no more than a few hundred people, in contrast to the crowds of 10,000 and up that flock to the ­mega-rallies of mogul Donald Trump and Sen. Bernie Sanders (Vt.).

Clinton almost never takes questions from his audiences. Instead, when he is finished speaking, he wades into them, lingering at the security barricades until the last person who wants one gets a selfie, a hug or an empathetic ear.

And he gathers intelligence. Campaign officials say he is in constant contact with Hillary’s Brooklyn campaign headquarters, sending back reports of what he is hearing from donors, activists and ordinary voters.

Running around the clock

Clinton’s Puerto Rico swing was a noteworthy investment in a territory that cannot even vote for president in the November election. But it will have 60 Democratic convention delegates at stake in its June 5 primary. The island and its issues also resonate with Hispanic voters across the country.

During a campaign stop in Kentucky, Democratic presidential candidate Hillary Clinton tells supporters she asked her husband, former President Bill Clinton, to come out of retirement to work on her jobs and manufacturing plan. (Reuters)

He has a feel for the ­blue-collar white voters with whom his wife has struggled to connect. With two days to go before the Democratic primary in Massachusetts on March 1, Hillary Clinton was gaining on Sanders in a state where he had been favored.

Charlie Baker, Hillary’s state director there, got a call from Tina Flournoy, Bill Clinton’s chief of staff, asking whether Democratic Rep. Jim McGovern might arrange an election-eve rally with the former president in McGovern’s working-class home town of Worcester.

But there was a catch: Clinton wanted to do it at 11:30 p.m.

As the clock ticked into primary election day, the former president lit a fire with the crowd in Massachusetts’s second-largest city, Baker said. “We probably would have lost Worcester if he hadn’t come.”

When the polls closed, Hillary Clinton had edged out Sanders by less than two points in the Bay State.

[Even supporters agree: Clinton has weaknesses as a candidate. What can she do?]

People who have not seen Bill Clinton in a while are sometimes surprised at the appearance of a man who will turn 70 in August. He is drastically thinner than he was in his days of gobbling Big Macs and doughnuts — a function of both time and the vegan diet he now follows as a heart patient.

When he first hit the trail for Hillary in January in New ­Hampshire, Clinton’s rustiness was obvious, the effect of eight years that have passed since his wife’s last campaign. His ­post-presidential endeavors have put him on a very different kind of stage, doing work for his foundation around the world and giving lucrative speeches before adoring audiences.

His stump speech sounded more like a TED talk. Clinton seemed to spend more time rhapsodizing about his own record than her vision; his voice at times was so raspy and weak that technicians had to turn up the volume to make him audible in a modest-size gymnasium.

Lately, he has hit his stride. In inner-city Baltimore on the Sunday morning before the Maryland primary, he preached from the pulpits of three African American churches, quoting the prophet Isaiah and the Book of James.

His presence there also displayed some of the personal ties he has built and nurtured over decades.

At Bethel AME, in a depressed neighborhood with block after block of boarded-up houses, Pastor Frank M. Reid III recalled the time when Clinton invited him to a White House lunch with Nelson Mandela, shortly after the South African leader was freed from prison.

“This man — no human being on earth is perfect — but this man has done a good job for the United States,” Reid said.

Yet Clinton does not confine his efforts to friendly territory. In Kentucky, he coolly handled jeers of coal miners and their families in the remote mountain town of Prestonsburg.

[Bill Clinton takes on protesters in coal country]

“I don’t mind being booed. I’m too old to worry about it,” he told them. “All I’m telling you is, go vote for who you want to. Do whatever you want to do. But don’t pretend that we can get anything done by screaming at each other.”

Five days later, his wife would lose that Kentucky county to Sanders by nearly 2 to 1. But after her husband’s (and her own) blitz of the state, including one day that Bill packed with four appearances, she pulled out a razor-thin victory.

Tallahassee Mayor Andrew D. Gillum was rushing to the airport one day in February when he got a phone call from the former president, whom he had never met. Gillum was inclined to stay uncommitted in the Democratic primary, he told Clinton, who then enlisted campaign chairman John Podesta to talk to Gillum as well.

By the time the tag team was finished, Gillum had agreed not only to endorse Hillary Clinton but to stump for her the following week in South Carolina.

Later, Clinton asked the ­36-year-old mayor to help him get to know other up-and-coming political leaders in Florida, a crucial swing state. Gillum arranged a private session in Orlando between Clinton and 20 young elected officials — many of whom were supporting Sanders.

“For an hour and 15 minutes, he sat there and listened to their thoughts,” Gillum said.

The upside and the downside

There have been times in the past — and may well be in the future — when it was unclear whether Bill Clinton was more an asset or a liability to his wife’s aspirations.

Early on, her team’s concern was that his star power would burn so brightly that it would put her in his shadow. But as her front-running presidential campaign was being overtaken by that of a first-term senator from Illinois in the 2008 Democratic primary season, her husband compounded her problems with churlish and undisciplined ­outbursts.

At one point in that year’s heated and bitter South Carolina primary, Sen. Barack Obama lamented, “I can’t tell who I’m running against sometimes.”

This time around — for perhaps the first time in his public career — Bill Clinton seems to be finding his groove within the narrow boundaries of a supporting role.

“In service of his wife, he is best used as a conventional weapon, deployed on these retail missions in swing states, rather than as a spokesman in the media, where he can be brilliant, but sometimes lets his emotions run away with him,” said David Axelrod, who was Obama’s chief campaign strategist.

“He’s also likely to be a collateral target of Trump, so these low-key assignments hedge against it becoming a shootout between them,” Axelrod added.

Nor does Bill Clinton appear to have any inclination to take the bait from Trump, the GOP nominee-apparent who has been dredging up the more unsavory chapters of Clinton’s past, both real and rumored, with increasing frequency.

Trump has gone so far as to call Clinton a rapist. As the former president made his way through the Lechonera El Mojito restaurant here, a reporter asked him to respond to a tweet by Trump earlier that day accusing him of being “the WORST abuser of woman in U.S. political ­history.”

“No, I won’t,” Clinton said brusquely. “I think people are smart enough to figure this out without my help.” Then he turned his back and moved on to shake a few more hands.

Still, Clinton can be thin-skinned, particularly when his presidential legacy is challenged, as it was by a couple of Black Lives Matter activists in Philadelphia. Though he had in the past said that the crime bill he signed in 1994 had gone too far, he erupted when the protesters made the same argument.

“I did something yesterday in Philadelphia I almost want to apologize for,” Clinton said the next day.

Part of the adjustment for Clinton comes from the fact that the Democratic Party in 2016 is significantly more liberal than the centrist one that he had reshaped in the 1990s. Hillary Clinton herself has moved away from some of the policies he championed — not only on criminal justice but also in areas such as free trade.

As he was making his way through a recent street concert in downtown Lexington, Ky., the band broke into Fleetwood Mac’s “Don’t Stop.” In 1992, it was his presidential campaign’s anthem of generational change; today, it’s a baby boom oldie.

Both Clintons have begun talking more about the role he might play as the spouse of a president who has also been a president himself.

It is a tricky issue, reminiscent of the stir the Arkansas governor caused in 1992, when he boasted that voters would be getting “two for the price of one” if they elected him president and brought his brainy wife to the White House with him.

Her subsequent foray leading his effort to transform the health-care system turned into a political disaster that helped cost the Democrats their majority in ­Congress.

She has indicated that she wants him to be involved with job creation: “I’ve told my husband he’s got to come out of retirement and be in charge of this, because, you know, he’s got more ideas a minute than anybody I know.”

In Kentucky, Bill Clinton said he also envisioned such a job for himself, though he too paints his role in vague and glossy terms.

“I was governor when the Ozark Mountains where I lived had three of the four poorest counties in America. I get this,” he said. “I know it’s hard when places are physically isolated. I’m not pretending. All I’m telling you is, I volunteer that if Hillary got elected president, I would like to be tasked with responsibility to take you along for the ride to America’s future.”

Or as they might have put it in another century: Don’t stop thinking about tomorrow.