Sen. Ted Cruz (R-Tex.) is among the potential 2016 Republican presidential candidates who has been reaching out to advisers and brushing up on policy recently. (Charlie Neibergall/AP)

Last Monday night at Washington’s Capital Grille, Senate firebrand and potential presidential candidate Ted Cruz met conservative economist Stephen Moore for a dinner that stretched on for four hours. Moore said he helped the Texas Republican brainstorm policies that would get beyond “standard Republican pablum.”

Marco Rubio (R-Fla.), another senator eyeing a 2016 run, recently summoned former Congressional Budget Office director Douglas Holtz-Eakin to his office and regularly solicits advice from scholars at the American Enterprise Institute.

And to get schooled on foreign affairs, New Jersey Gov. Chris Christie (R) has been consulting former secretaries of state Henry Kissinger and Condoleezza Rice, as well as Council on Foreign Relations President Richard N. Haass.

It’s all part of what might be called the “credentials caucus” — the period before the 2016 campaign when the Republican Party’s presidential aspirants quietly study up on issues and cultivate ties to pundits and luminaries from previous administrations.

“Presidential candidates have a lot to not just learn, but to decide,” said Michael Leavitt, a former Utah governor and George W. Bush Cabinet member. “They have to develop a cohesive and consistent point of view on various issues that they probably never had to think about before.”

Over meals, on the phone and in one-on-one chats, the rivals are building relationships with people they hope to recruit to help them navigate a range of issues. Policy leaders are generally hesitant to align with a candidate this far out, but the meetings send signals to would-be donors and operatives about the seriousness and direction of a potential candidacy.

Most of the 2016 hopefuls are networking within an entrenched community of conservative professionals who rose to prominence in the Nixon, Reagan or Bush eras. Some advised George W. Bush in the late 1990s as he mulled a White House bid or helped Mitt Romney, the GOP’s 2012 nominee, develop his policy prescriptions.

With the exception of some voices within the circle of libertarian-leaning Sen. Rand Paul (R-Ky.), those being tapped hew to Republican norms on foreign policy, with emphasis on a vigorous military and a willingness to use force overseas. On domestic policy, the Republican mantra of slashing federal spending and loosening regulations remains the consensus view. At the same time, many in the potential field are seeking to incorporate fresh perspectives to appeal to an increasingly diverse electorate, including talk of combating income inequality — an issue largely championed by Democrats.

For some of the Republicans planning a path to the nomination, the learning process is imperative. With the exception of former Florida governor Jeb Bush — who said Sunday that he will decide by the end of this year whether he will run — the GOP contenders are policy novices compared with the leading Democratic prospects, former secretary of state Hillary Rodham Clinton and Vice President Biden.

The consultations, which are happening out of public view, were confirmed in interviews with dozens of Republican officials, policy advisers and political aides.

In this early stage, Rubio seems furthest along, crystallizing his views with a series of speeches, including one critical of “isolationists” and another touting his ideas on college affordability. His chief of staff, Cesar Conda, and deputy chief of staff, Sally Canfield, have long policy backgrounds, as does Jamie Fly, a fierce critic of President Obama’s foreign policy who was hired by Rubio last year.

Rubio routinely invites policy experts to his office for conversations and his staff regularly sends articles and research papers to a drop box titled “upward mobility” on his computer.

“If I’m just going to come here and have talking points, the experience isn’t rewarding,” Rubio said in an interview. “I really believe Republicans have to start to be more than the opposition and think about how best to talk about our alternatives.”

Rubio has become friendly with Yuval Levin, who has published widely circulated essays on domestic policy in National Affairs. He has also broken bread with Ross Douthat, the 34-year-old New York Times columnist who advocates a middle-class agenda.

But Rubio said that the American Enterprise Institute is the “primary organization” he turns to. He confers with the group’s president, Arthur C. Brooks, who hosted him in January for a speech on poverty, as well as with columnist (and one-time “Jeopardy!” champion) James Pethokoukis.

Former defense secretary Donald H. Rumsfeld, known for his controversial decisions during the Iraq war, has been courted by several potential candidates and plans to meet with Cruz. Cruz has hired former Rumsfeld aide Victoria Coates as his national security adviser.

Many 2016 contenders have a single aide or ally coordinating their dialogue with conservative academics and White House alumni. Venture capitalist Robert E. Grady, an associate budget director in the George H.W. Bush administration, does so for Christie.

“Consistency is really important,” said Beth Myers, a longtime adviser to Romney. “You don’t want to be out on the road making mistakes.”

Wisconsin Gov. Scott Walker (R) met in California last year with scholars at Stanford University’s Hoover Institution, including former White House economic adviser John B. Taylor and former Romney policy director Lanhee Chen.

Walker is doing more prep on global issues and has developed a bond with Washington Post columnist Marc A. Thiessen, a former George W. Bush speechwriter and a foreign policy hawk. In 2013, when Thiessen helped Walker write the governor’s memoir, they talked via Skype about many issues.

Rep. Paul Ryan (R-Wis.), the 2012 vice presidential nominee, has deep contacts throughout the policy arena. Ryan is close to former education secretary William J. Bennett and a constellation of right-leaning thinkers, from the Hudson Institute’s social policy analyst William Schambra to community organizer Bob Woodson, who has traveled to urban areas with Ryan. In March, Ryan had dinner with Holtz-Eakin at the Occidental, a restaurant near the White House.

Louisiana Gov. Bobby Jindal (R), meanwhile, is trying to position himself as the field’s wonky problem-solver. The former Rhodes scholar says he wants to “win the war on ideas” and started a nonprofit group, America Next, to publish white papers.

After unveiling his health-care plan last week, Jindal sat for two hours in a Washington office building to get feedback from conservatives including Levin, Weekly Standard editor Bill Kristol and National Review senior editor Ramesh Ponnuru.

Jindal also has been courting Heritage Foundation President Jim DeMint. Ethics laws bar DeMint, a former senator from South Carolina, from discussing politics with federal legislators so soon after leaving office, but he can meet with state governors. In late March, DeMint huddled with Jindal at a hotel in New Orleans, where the governor talked up DeMint’s policy work.

When they visit Washington, many governors stop by key gatherings, including the Saturday Evening Club, a monthly dinner hosted by the American Spectator, a conservative magazine, and off-the-record Wednesday breakfasts run by anti-tax activist Grover Norquist.

Moore, a former Wall Street Journal editorial writer and zealous tax-cut advocate who is now at Heritage, has advised Cruz and Rubio. He also has arranged dinners with economists for Paul at the Monocle restaurant on Capitol Hill.

“They’re all struggling to find the right message that doesn’t sound stale,” Moore said.

Other Heritage scholars, including national security specialist James Carafano and former senator Jim Talent of Missouri, have become a faculty of sorts for potential candidates whose foreign policy views lean toward the conservative end of the GOP spectrum.

“There are people who are important in the party apparatus or important donors who have an interest in at least some area of foreign policy, and it’s important as you interact with them to sound knowledgeable,” said Talent, who advised Romney on defense issues.

After stumbling on policy matters in 2012, Texas Gov. Rick Perry (R) has been getting briefings from think-tank experts and other former Republican administration appointees. During a trip in October to Israel, he met with Prime Minister Benjamin Netanyahu, and he has visited with foreign government and business leaders in London and at the World Economic Forum in Davos, Switzerland.

Paul, who has made several trips to Silicon Valley, is connecting with tech leaders who offer him policy advice. Paul met last month with Microsoft founder Bill Gates at the Dirksen Senate Office Building and has spoken multiple times with PayPal co-founder and libertarian donor Peter Thiel.

Paul also talks with Richard Burt, a former Reagan ambassador, and Lorne Craner, a former State Department official in both Bush administrations — outreach designed to show that he’s not a lonely dove.

On foreign policy especially, the potential candidates are still learning. A frequent counselor is Sen. John McCain of Arizona, the GOP’s 2008 nominee.

“They all call, all the time, even if some of them are just checking the box,” McCain said. “First, I tell them to touch base with Henry Kissinger — of course.”

Not every senator is consulted as a sage, however. Sen. Charles E. Grassley (R-Iowa), a former finance committee chairman, said the contenders ask him about Iowa campaigning, not fiscal policy.

Grassley recalled with a sigh that the most substantive exchanges he had with presidential candidates were in 1976, when he was a House member and Reagan and Gerald Ford reached out. “Those calls — even if they were courtesies — were wonderful,” he said.