No one, however, may be more valuable to a Romney administration than Sen. Rob Portman (Ohio). He has experience in the House, knows the budget and tax issues as well as anyone outside of Ryan and has the respect of and credibility with Democrats, aides and fellow lawmakers told Roll Call.
Although Portman doesn't have a powerful chairmanship, he's trusted by his Conference, is very close to Romney and was on the nominee's very short list for vice president.
Portman told Roll Call earlier this week that he wants to stay in the Senate rather than join a Romney cabinet, suggesting that his experience would be best suited to navigating legislation through that chamber. He's already discussed the intricacies of the Senate reconciliation process with Romney.
Sen. Roy Blunt (Mo.), the Romney campaign's liaison to the Senate, also has a lot of experience as the former House Majority Leader and Whip; he's a consummate dealmaker who knows how to make the trains run on time. Blunt has a keen political sense and navigated the bruising intraparty battles the last time the GOP held the House, the Senate and the presidency.
Sen. Mike Crapo (Idaho), a senior member of the Finance Committee who is one of the Senate's most respected leaders on budget issues, also gets mentioned as someone who will play a larger role in the chamber.
Former Sen. Jim Talent, a Romney surrogate, said some of the younger Republicans will help push Romney's agenda beyond the obvious players chairing committees and in the leadership.
"These new and very aggressive and dynamic Senators, everybody from a Rubio to a Portman, to a Roy Blunt, and Ron Johnson" will give energy to the administration's efforts, Talent said. "There are a lot of people even thought they are new to the Senate [who] are very accomplished in getting a reform agenda done, and Rob [Portman] is one, Roy [Blunt] is another obviously; I think Rubio's hit the ground running there, and Johnson has too. There's a lot of those people."
He continued, "And then you are going to have people who have been there for a long time, and want to do things and haven't been able to do it - your Mike Crapos, people like that, and I think you'll see them stepping up to."
RNC spokesman Sean Spicer said Ryan's selection also will help Romney get the ball rolling.
"You've got a lot of former House Members in the Senate now ... so he's got a lot of those guys that he's worked with, and he's close to the leadership as well," said Spicer who named Sens. John Thune (S.D.), Richard Burr (N.C.) and Portman and Blunt.
"Romney already has a lot of relationships on the Hill but Ryan's got a lot of connections that will add some firepower to Hill outreach," Spicer said.
Spicer pointed to Camp as someone likely to be particularly helpful.
Former Sen. Scott Brown, R-Mass., candidate for U.S. Senate in New Hampshire, holds his hand over his heart during the singing of the national anthem as he waits to take the stage for his town hall campaign rally with Sen. John McCain at the Pinkerton Academy in Derry, N.H., on Monday, Aug. 18, 2014.