Like a proud father looking to relinquish control of the family business, Sen. John McCain is pushing soft-spoken Sen. Rob Portman to take a more assertive leadership role on Capitol Hill.

Long impressed with Portman’s policy expertise and agreeable demeanor — “It’s a trait I wish I had more of,” the often-prickly Arizona Republican said — McCain strongly urged Senate Minority Leader Mitch McConnell (R-Ky.) to appoint the Ohioan to the Joint Committee on Deficit Reduction and continues to encourage his freshman GOP colleague, at times rather strongly, to be more aggressive.

This isn’t the first time that McCain, his party’s 2008 presidential nominee, has taken an interest in a new Member. The 75-year-old identified Sen. Lindsey Graham (R-S.C.) as an up-and-comer soon after he arrived in the chamber, and the two are now personally close and joined on many issues.

After five terms in office, McCain indicated his star is on the wane, but he appears intent on finding a successor to replace him on the national stage.

During an interview with Roll Call last week, McCain offered that his career is on the “downside.” He said of his colleague from Ohio: “I wouldn’t say he needs mentoring on how this place works. I would just say that I’ve tried to encourage him to take the leadership role that he’s qualified for.”

As he pushed back against the notion that he is a “mentor,” the Arizona Republican said seniority plays less of a role in the Senate than it did years ago. He said his goal is simply to recognize new Members who are ready to contribute right away and help them do so by advising them directly and putting the word out to veteran Senators that they should be taken seriously.

McCain and Portman, 55, have known each other for quite a while, dealing with each other on budget and other fiscal matters during the former House Member’s service as President George W. Bush’s budget director — from May 2006 to June 2007. The two Senators have long shared an interest in budget issues, which has served as one of the foundations of their relationship.

In 2008, Portman played then-Sen. Barack Obama during McCain’s presidential debate rehearsal, with the Arizonan describing the Ohioan’s performance this way: “He played the role of Sen. Obama in the most infuriating fashion.”

Portman quipped that his performance was so effective, “I wasn’t very popular in the McCain family” at the time.

McCain, who easily won re-election last year, campaigned for Portman in 2010 and then lent him the use of his coveted Capitol hideaway early in the year until the Ohio Republican’s permanent office in the Russell Senate Office Building was ready. Portman confirmed that his Arizona colleague has pushed him to step up — particularly on fiscal and economic issues — since he arrived in the Senate in January.

Just days before the early August vote to raise the debt ceiling — with partisan tensions running high — McCain forcefully urged Portman to act like a Senate veteran and take a more prominent leadership role on budget matters. The private 15-minute conversation occurred as the two exited the weekly GOP Conference lunch and walked back to their respective offices, and it happened the day after McCain delivered a stinging critique of the tea party on the Senate floor.

“He’s been encouraging me to use my background to try to promote fiscally conservative positions, which I’m doing,” Portman said. “I really appreciate him and the role he continues to play as a senior statesman. He could be sitting back and kind of allowing the legislative process to move on without him. As you know he’s very aggressive, very assertive. It’s good for the Conference and good for our country.”

McCain noted, “I don’t know anybody who knows the numbers and has the vision that Rob Portman has.”

Portman said McCain’s background as a former Republican presidential nominee, his military experience and his longevity in the Senate make him uniquely suited to the role of pushing and encouraging promising young Members.

McCain said that, in addition to Portman, he also sees freshman Republican Sens. Kelly Ayotte (N.H.) and Marco Rubio (Fla.) as Members with great potential.

Graham, now approaching a decade in the Senate, said McCain’s tutelage offered him opportunities to get involved in legislation that would be taken seriously because of the Arizona Republican’s stature. He also said he appreciated being able to develop a personal relationship with a key Member in a chamber that runs on such connections. Graham predicted that Portman would benefit similarly.

“What turned into trying to help me understand the Senate and get involved in legislative issues turned into a real friendship. … The body is a very personal, relationship-driven body,” Graham said. “Rob has unlimited potential, and John is seen by our Conference as someone who is listened to when he talks, and anything that Rob and John can do together is going to increase the likelihood of passage of that particular piece of legislation.”