Former New York mayor Rudolph Giuliani speaks in New York in 2014. (John Minchillo/Associated Press)

Fresh off back-to-back victories in the Republican presidential race, Donald Trump is moving to expand his tight-knit campaign by building a political kitchen cabinet that includes former New York mayor Rudolph W. Giuliani.

Giuliani, who has not made an endorsement in the 2016 contest, said in an interview Sunday that he has conferred at length with Trump at least three times in the past month, both in person and by phone, and has counseled the real estate mogul “as a close personal friend” about campaign issues.

“We’ve been talking. Donald and me, Donald and a few other friends who know politics. He calls to check things out or I’ll call him to say, ‘Donald, you’re going too far’ or ‘What you said was great’ or maybe ‘Change it a bit.’ It’s nothing formal. It’s kind of a running conversation,” Giuliani said. “There is candor and there is trust.”

Giuliani would not disclose who else has been speaking more frequently with the GOP front-runner. But he said there is a growing group of high-profile New York and Washington-based figures with deep GOP ties who are now in regular touch with Trump and quietly connecting his campaign with their own networks.

“I could easily list off some names for you but that’s for Donald to say,” Giuliani said.

In an email Sunday night, Trump confirmed that Giuliani has become part of his inner circle as he navigates the 2016 terrain and hotly contested primaries.

"Rudy is a very knowledgeable friend. I consider his counsel very important," Trump wrote.

Donald Trump won the Feb. 20 South Carolina GOP primary. Here's how. (Peter Stevenson/The Washington Post)

Trump’s effort to create a private sounding board of associates and allies is the latest example of how he is broadening his outreach beyond the small team of policy aides who work on his campaign. And it underscores how the Republican establishment, which once firmly opposed his candidacy, is beginning to have warmer relations with the candidate, especially as his chances of clinching the nomination improve with each primary win.

Giuliani, 71, ran unsuccessfully for the GOP nomination in 2008 but remains popular with many Republicans for his leadership in the aftermath of the Sept. 11, 2001, attacks.

Giuliani described his talks with Trump as “frank” but encouraging. “I think he could over perform in a general election similar to what Reagan did in 1980, bringing in new people,” he said. “He has that ability. On the other hand, I’ve told him when I’ve disagreed, telling him when I think he may be hurting himself.”

Giuliani mentioned Trump’s criticism of former president George W. Bush at a recent debate as one particular area where they do not overlap. “I thank God that George W. Bush was president during 9/11,” he said.

“The way this works is that it’s an open line, him to me, me to him, him to others. He is calling a lot of people, listening but doing what he thinks he needs to do. He listens respectfully, says he’ll consider whatever it is you send him. Sometimes he uses what we send him, sometime he doesn’t,” Giuliani said.

“You know, he’s very good,” Giuliani said when asked about Trump’s grasp of complex policy. “It’s clear that he has an exceptionally good understanding of how the economy affects our foreign policy. He understands what’s happening with China, how they could stop North Korea in a heartbeat. This idea that he’s only familiar with slogans, it’s not accurate at all.”