Two former big-city mayors named Michael will be hitting the 2020 campaign trail together.

Former Philadelphia Mayor Michael Nutter will be national political chair of billionaire Michael Bloomberg’s 2020 presidential campaign, Nutter said Thursday — a prominent addition to the growing network of mayors who support Bloomberg’s late entry into the Democratic race.

To date, Bloomberg, a former three-term mayor of New York City, has backing from nine mayors, including the chief executives of San Jose, Calif.; Louisville, Ky.; and Columbia, S.C. Nutter is the first former mayor to endorse him.

Bloomberg, who joined the race in November, was polling nationally at about 5% this week, ahead of several candidates who have been campaigning for more than a year. He’s broken campaign spending records, pouring more than $100 million into ads since Nov. 25. He’s also relying in part on the support of influential city leaders who have, in the past, benefited from Bloomberg Philanthropies grants for initiatives in their cities.

“Mike Bloomberg has been a friend, adviser, supporter, and certainly a mentor from the day we met,” Nutter said in an interview. “These are extraordinary times and I think they require an extraordinary response. People want leadership...and are really looking for significant change. I think Mike brings that change.”

A moderate Democrat who also has supported Republicans in Pennsylvania, Bloomberg will be in Philadelphia on Saturday for the opening of his first field office in the state, near Independence Hall. The office will be about a mile from former Vice President Joe Biden’s national headquarters. Bloomberg’s campaign will prioritize battleground states during the primary.

“Michael Bloomberg is obviously spending significant resources in a variety of places and ways, unlike any other campaign seeking the presidency," Nutter said. “He’s going where some of the campaigns are not going.... He’s running a general election campaign during the course of the primaries.”

Bloomberg’s primary strategy is different from his Democratic rivals. He entered too late to qualify for the December or January debates or to make significant inroads in the early voting states. But with a near-endless cash supply, Bloomberg is instead focusing on Super Tuesday, where more than one-third of all Democratic primary delegates will be up for grabs.

(The first voting states, Iowa, New Hampshire, South Carolina and Nevada, where most campaigns have focused their energy, account for close to 4% of delegates.)

Nutter, who led Philadelphia from 2008 to 2016, has known Bloomberg for more than a decade, collaborating with him when the two were mayors. Nutter himself has worked at What Works Cities, a project of Bloomberg Philanthropies, as a senior fellow and spokesperson since 2016.

Philadelphia has received several million dollars in Bloomberg grants over the years. The city was one of 20 to win a slice of a $70 million grant to address climate change and the recipient of a $1 million Mayor’s Challenge grant to create a program to help juveniles entering the criminal justice system cope with trauma.

Bloomberg also helped fund a $1 million information campaign in radio and TV ads touting the benefits of Mayor Jim Kenney’s sweetened-beverage tax before it passed in 2016. (Kenney endorsed Massachusetts Sen. Elizabeth Warren last month.) Ed Rendell, the former governor who was mayor of Philadelphia in the 1990s, is a prominent Biden backer.

In April, Nutter co-hosted a fundraiser for the former vice president, giving the maximum $2,800 donation to his campaign. Nutter said Thursday Bloomberg had always been his first choice.

“When Mike was talking about running earlier this year, I had a couple conversations with him at that time, and I strongly encouraged him to run,” Nutter said.

As national chair, Nutter will coordinate national political activities and meet with politicians and work with coalitions. Neither Nutter nor the campaign would say what he’d be paid for the position. Nutter said he will keep teaching positions at Columbia University and the University of Pennsylvania.

“I think part of the challenge here is, what do people know about him?" Nutter said. “He used to be mayor, he’s a business guy and a philanthropist, and that’s about it. So part of the challenge for any candidate is, how do you get your message out about who you are, what you’re going to do?”

Nutter first met Bloomberg in August 2007, when Bloomberg was a newly registered independent; he was a Republican when first elected mayor of New York. Nutter had just won the Democratic primary for mayor in Philadelphia and wanted to visit other big-city mayors to get a sense for what was in store before taking office.

Bloomberg and Nutter later collaborated on Mayors Against Illegal Guns, now called Everytown for Gun Safety. Philadelphia also modeled a program for startup businesses after a similar one in New York City. Conversely, New York City modeled a mortgage foreclosure prevention program after Philadelphia’s.

Bloomberg, the former three-term mayor of New York City, has faced criticism particularly from some African American leaders for his implementation of stop-and-frisk policing as mayor — a position he has since apologized for. As co-founder of Bloomberg L.P., a global financial services, software, and mass media company, Bloomberg became the ninth richest person in the United States, worth an estimated $58 billion as of November. He’s given at least $8.2 billion of his wealth away.

On the campaign trail, Bloomberg has spent an average of $3.72 million per day on ads, according to Advertising Analytics. He’ll have enough funds to broadcast commercials in Super Tuesday states, including California, a costly undertaking — and to open field offices in them.

“When we land on the ground in a variety of places, we’re not coming for a visit and leaving,” Nutter said. "We’re staying.... And no one [else] has the resources, quite honestly, to be able to do that.”