As Joe Donnelly prepares to take up his position as the new U.S. ambassador to the Holy See, one former diplomat has some advice: Build relationships in the Vatican.

Peter Martin, now working at Boston College, is the longest-serving U.S. diplomat accredited to the Holy See since the formal relations were established between the United States and the Vatican were established in 1984. He was in Rome for stints –from 2003-07 and 2014-17 – and worked under three different ambassadors: Jim Nicholson, Francis Rooney, and Ken Hackett.

“I found each of my ambassadors to be effective in different ways. It isn’t so surprising when each was so successful in his previous career – all of them in different fields. I think lessons from each of them would be useful to anyone going to a diplomatic posting at the Vatican,” Martin told Crux.

Nicholson was George W. Bush’s man in the Vatican, and was ambassador during one of the most turbulent times in the relationship between the two states, when the U.S. invaded Iraq, a move that was strongly opposed by Pope St. John Paul II.

Nicholson had a very close relationship with Bush, having served as the Republican national party chairman during his successful 2000 election campaign.

Martin noted that this personal touch was important.

“In one instance, the Holy See came to us to ask for our help on an issue regarding Russia. Now, as a foreign service officer, I can – and did — write a pithy cable back to Washington after a meeting like that, sending it as a top priority to the State Department. But that’s never going to do as much as Ambassador Nicholson did when he called President Bush directly to discuss the issue. We were later told that the issue got right into the president’s talking points for his upcoming meeting with [Russian President Vladimir] Putin,” he said.

Martin told Crux that each ambassador he worked with had lessons that would help Donnelly in his role.

“Ambassador Jim Nicholson had an amazing ability to analyze and understand a bureaucracy. He arrived in Rome with a good understanding of the domestic Church, but without a lot of experience with the complicated and not always intuitive structures of the Roman Curia,” he said.

“However, he got to work and simply mastered that labyrinthine system. He always knew whom to speak to in order to move an issue forward, and whom we should work with in order to create synergy, and not antibodies. That isn’t always easy at the Vatican,” Martin explained.

“He was also a great leader; he set clear and attainable goals for what he wanted to accomplish. He had everyone rowing in the same direction. For example, early in his tenure, there was a lot of media attention to the Holy See’s opposition to the U.S.-led invasion of Iraq. However, when that decision was in the rearview mirror, Nicholson pivoted and set us up to pursue four specific initiatives with which we could amplify U.S. priorities with Holy See interest and support, changing the narrative and doing some good. Among them was an increased spotlight on religiously inspired terrorism, as well as a concentrated effort to combat human trafficking before it was fashionable to do so. We made real contributions because of his vision,” he added.

After Nicholson was appointed to Bush’s cabinet as Secretary for Veteran Affairs, he was replaced by Francis Rooney, a prominent Republican businessman.

Martin recalled he brought a “fresh set of eyes” to the embassy, and wasn’t satisfied when people told him, “We’ve always done it this way.”

“As an action-oriented businessman, he also refused to be constrained by the sometimes slow-moving U.S. government bureaucracy and always found a way to get things done,” he said.

He added that Rooney’s creativity paid important dividends for the U.S. mission to the Vatican.

“In one case, he had us arrange a day-long conference on interreligious dialogue and reconciliation in Sarajevo with Cardinal Vinko Puljic, the city’s archbishop. Many at [the State Department] would have shied away from engagement on another embassy’s turf, but Rooney saw an opportunity and convinced our embassy in Sarajevo – and Puljic — of the worth of the venture. He then invited Vatican officials to travel with us to Sarajevo, raising the profile of the effort considerably. The conference and side meetings aided reconciliation efforts in the region and the day was also a great example of the convening power and multiplier effect of our embassy,” Martin said.

The former Vatican diplomat also said Rooney also knew how to use his strengths, including his knowledge of Latin American politics and culture.

“He downplayed his Spanish language skills, but he was actually a good Spanish speaker who was extremely effective in developing relationships with the strong Spanish-speaking contingent within the Curia and Vatican diplomatic corps,” Martin said.

“He capitalized on these skills by making attention to Latin America one of his priorities as ambassador. Gaining support from Washington, he found common ground with the Holy See on several regional issues, including the promotion of democratic values and attention to human rights.”

Martin left the Holy See embassy in 2007 but returned in 2014 to work under Ambassador Ken Hackett.

Unlike the Bush appointees – who were Republican Party insiders – President Barack Obama’s pick was a Catholic Church insider, having previously served as the head of Catholic Relief Services, the international development arm of the U.S. bishops’ conference.

“Of course, Ambassador Ken Hackett brought with him years of experience with the global church from his days with Catholic Relief Services,” Martin told Crux.

“One of the great lessons to be learned from him is the importance of relationships. Vatican officials liked and trusted him. And if they didn’t know him yet, they soon realized that they had friends and colleagues in common,” he said.

“As Ambassador Hackett recently told my class at Boston College, when he first met the current Holy See Secretary for Relations with States, Archbishop Paul Gallagher, he reminded Gallagher that the two had met years before in Burundi, when Gallagher was papal nuncio there and Hackett was with CRS. But Archbishop Gallagher reminded Hackett that they had actually worked together years before that, when Gallagher was at the nunciature in Manila and Hackett was the CRS country director for the Philippines. Thus continued a very effective working relationship that included preparations for the visit of Pope Francis to the United States in 2015 and consultation on numerous global crises,” Martin said.

He noted that the U.S. Embassy to the Holy See has often been called a global listening post because Rome and the Vatican are such a crossroads for people from all over the world, adding that was never more true than under Ambassador Hackett.

“When bishops from any country in the Global South came to Rome for their quinquennial ad limina visits, Ambassador Hackett seemed to know half of the men who were getting off the bus at Santa Marta,” Martin remembered.

“It’s important to realize that bishops from places where the Church is embattled or where there is a difficult political situation may not want to engage with the U.S. embassy in their home country for fear of attracting unwanted attention. But when they saw Ambassador Hackett, many were eager to engage with us in Rome. We would discuss shared priorities with the U.S. government and exchange views on any number of issues. It was an important way to further U.S. foreign policy goals, all because of relationships,” he said.

Martin noted the unique set up in the United States, where many of ambassadors are “political appointments” as opposed to career diplomats, which is the case for most other countries.

“Some observers of U.S. foreign affairs complain about political appointee ambassadors, but I often recount episodes from my work with these ambassadors to make the point that political appointees have certain advantages. All three of these ambassadors were very well regarded in Washington. Ambassadors Nicholson and Rooney had very good relationships with President George W. Bush. This can be very important,” he said.

Follow Charles Collins on Twitter: @CharlesinRome