Paul D. Ryan’s years spent honing his fiscal expertise and cultivating relationships will assure his ascent to the speakership this week — and immediately plant a numbers pro in the middle of high-stakes budget talks.

The negotiations, however, also threaten to tear apart the delicate political mandate Ryan has assembled within the House GOP.

Though the Wisconsin Republican has never served in leadership, there may be no House Republican more qualified to shape the fiscal 2016 budget deal, by some accounts. And he could be a significant addition to deliberations that, by participants’ accounts, are drifting in advance of the Dec. 11 end of the short-term continuing resolution.

Ryan arguably understands the budget better than anyone else in Congress. He was the chief Republican negotiator of the last budget deal (PL 113-67), the two-year agreement that he reached with Sen. Patty Murray to raise the discretionary spending caps in December 2013.

While that agreement has its critics on the left and right, Ryan accomplished what some thought impossible: a plan for raising the discretionary spending caps that did not accede to Democratic demands to close tax breaks as part of the pay-for but still won Democrats’ support.

Moreover, Ryan – who has been demonized by some on the left – established a genuine friendship with Murray. The Washington Democrat is a hard-nosed politician and tough negotiator in her own right.

Republicans are enthusiastic. But some Democrats, too, are welcoming Ryan to his new role. “I’m a Paul Ryan fan,” said Senate Minority Leader Harry Reid, D-Nev. “I think what he’s done with Medicare and Medicaid, what he’s wanted to do, I disagree with. But generally speaking, I think that we’ve been able to work with him.”

House Democratic Whip Steny H. Hoyer is more skeptical. “Paul Ryan is about to become speaker and he is going to have a very early test both on debt limit and on budget as to whether or not he is going to lead in a pragmatic, effective way or he’s going to lead in a way that is ill-conceived and unrealistic,” the Maryland lawmaker told a small group of reporters Friday.

Hoyer said Ryan is “very articulate, very good at explaining actions. But his budgets were never realistic budgets and they were never implemented.”

2013 Deal Background

House Appropriations Chairman Harold Rogers, no slouch himself when it comes to dealmaking, said Ryan’s experience crafting the 2013 agreement has prepared him for the current budget talks. “This time we’ve got somewhat similar circumstances,” the Kentucky Republican said. “We’ve got the White House to deal with, Senate, House Democrats and the like.”

Rogers praised Ryan as a “very adept negotiator.” He said if anyone can bridge the gap between hard-line Republicans and the rest of the conference, it is Ryan.

Ryan, along with being a policy wonk, is “very bright, very agile, mentally agile, understands all sides, understands that you can’t get 100 percent of what you want in these kinds of deals,” Rogers said. “You have to take what you can get, what’s politically possible.”

Mick Mulvaney, R-S.C., who used to sit on the Budget Committee with Ryan and is also a member of the House Freedom Caucus, supports that view and is optimistic about Ryan’s prospects.

“I think it’s absolutely imperative that the first thing that has Paul’s stamp on it is at least a little better than it would have been if [House Speaker John A.] Boehner were here,” Mulvaney said. Mulvaney said he thinks that first thing will be “the CR-omnibus, whatever it is, at Christmas.”

Mulvaney said he wants to be able to demonstrate to his constituents down the road that Ryan produced an outcome that was better than what they would have had under Boehner, who is expected to resign at the end of the month.

“Maybe it was not great, it was not perfect, it’s not what you wanted,” he said he hopes to be able to say after the next budget deal. “But we weren’t going to get what you wanted, we weren’t going to get perfect. But we got better and that’s what we were shooting for. I think that calms everything down.”

Six Weeks

Ryan nevertheless faces a formidable challenge.

He will be stepping into budget talks in midstream and seeking to negotiate a deal that serves the conflicting interests of defense hawks and fiscal hard-liners, Democratic lawmakers and the White House.

And he will have just six weeks until Congress faces a government shutdown when the continuing resolution (PL 114-53) expires.

Ryan’s eight years as the top Republican and then chairman of the Budget Committee and his recent experience at the helm of the Ways and Means panel provide some insight into how he may handle the talks.

Over the past decade, Ryan’s fundamental views on federal spending and revenue have remained relatively unchanged. In his budget blueprints he’s advocated steep cuts to domestic programs, including converting Medicare to a voucher program, all in the name of keeping the programs solvent.

His budget resolutions earned accolades from the right but anger from Democrats, critiques that the left magnified during his campaign for vice president in 2012 as Mitt Romney’s running mate. Ryan has been steadfast against a “grand bargain” that raises taxes.

Still, Ryan has shown a willingness to make subtle changes to his plans and address the prevailing political currents. When Republicans won the majority in the House in late 2010 and Ryan became Budget chairman, he dropped some of the more controversial provisions in his earlier fiscal proposals, including a plan for partial privatization of Social Security and a tax credit aimed at encouraging individuals to buy health insurance.

More recently as Ways and Means chairman, Ryan partnered with Democrats and the White House to shepherd trade legislation (PL 114-26, PL 114-27) and the so-called “doc fix” (PL 114-10) that ended scheduled cuts to Medicare reimbursements for doctors.

He has been unable to achieve one of his biggest policy goals, a comprehensive rewrite of the tax code, something he has said is unrealistic while Obama is president.

In the meantime, it’s unclear how much of a honeymoon Ryan will have to set up his agenda while also tackling must-pass issues such as appropriations bills. “I don’t know that it’s going to be the honeymoon suite. It might be some economy version,” said Matt Salmon, R-Ariz., a Freedom Caucus member, when asked how much of a grace period Ryan would receive.

George Cahlink and Ryan McCrimmon contributed to this report.