At this time next year, it’s possible Eric Fehrnstrom’s telephone number will be among the most valuable commodities in Washington, D.C.

The Republican consultant is serving as a senior political adviser to presumptive GOP White House nominee Mitt Romney and Sen. Scott Brown (R-Mass.). If both candidates manage to survive tough battles and win in November,
Fehrnstrom might be in the unique position of having both the president and an influential Senator on speed dial. In a town that determines power according to access and relationships, Fehrnstrom would rank.

“Not only would he become the next Karl Rove on a national scale, he would be sought after as the Republican operative who cracked the code in the Northeast,” a D.C.-based GOP operative said.

Fehrnstrom was Brown’s key adviser in his upset special election victory in January 2010 — a campaign that shocked the political establishment of both parties. But Fehrnstrom’s relationship with Romney goes deeper than consultant-candidate, described by some Republican operatives familiar with the dynamic as similar to the role Karen Hughes played in the world of President George W. Bush. Hughes, a former journalist like Fehrnstrom, started with Bush when he was governor of Texas.

Fehrnstrom has been with Romney since his 2002 Massachusetts gubernatorial campaign, he was by his side when he first ran for president in 2008, and he is with him again during this contentious race.

He has acted as the gatekeeper to Romney as the governor’s world of consultants and aides has expanded beyond his tight, Boston-based inner circle, and he functions as an encyclopedic source for the campaign team any time questions arise about the candidate’s political or biographical record.

If there’s an inquiry about what Romney thinks and he’s unavailable to answer the question, Fehrnstrom probably can — and often does. GOP operatives who have observed their relationship say he doesn’t just have Romney’s “trust” and his “ear” — they say he’s earned both. Romney “values his advice and calls on it,” one Republican said. Fehrnstrom “has been with the governor a long time and knows him well.”

But playing a crucial role in two high-profile campaigns has brought challenges and thrust Fehrnstrom onto the national stage. Although known for sparring with the Bay State press during Romney’s single gubernatorial term, he had cultivated  a subtle presence in the 2012 campaign.

Fehrnstrom declined to comment for this article, responding to Roll Call only with an email in which he said: “I really do think these elections are about the candidates, not the hired help.” Still, his preferred low profile has been increasingly difficult to maintain.

Fehrnstrom’s work for both the likely Republican presidential nominee and an incumbent Senator in one of the most targeted races of the cycle has caused angst in some GOP circles.

“Mechanically, when you’re running one of the most expensive and highly watched Senate races in the country, when you’re involved in that type of race, it’s tough to do that and a presidential race at the same time,” said a Republican political consultant familiar with Massachusetts politics. “If it ends up being $20 million spent just on the Brown side and let’s say $15 million of that is TV. I mean, you’ve got to make 15 to 20 ads, at least, in a short period of time and you can’t just wave a magic wand to do that.”

But those aware of Fehrnstrom’s work said he’s capable of juggling two big campaigns with sometimes competing messages that are offered by candidates with differing personalities. Romney presents the image of the prototypical Northeastern politician — dry and formal; Brown is the charismatic everyman — likable and easy to relate to.

“[Fehrnstrom is] an extremely talented guy and I have no doubt that he’s going to be able to take care of his responsibilities with the Romney campaign and also work with Scott Brown,” a top Republican strategist said. “If Romney headquarters were in Washington, D.C., it might be more of a challenge, but they’re all in Boston. It’s in his backyard.”

With Beth Myers and Peter Flaherty, Fehrnstrom is part of the Shawmut Group, a public affairs and political consulting group based in Chesnut Hill, Mass. The group helped with a series of political races in November 2010, but with limited success.

Political consulting was a relatively new game for him.

“He wasn’t really seen as a political operative until recently,” said the GOP consultant familiar with Massachusetts. “He was seen more as a flack who did some campaigns, but mostly government stuff.”

But Fehrnstrom is definitely a prominent political operative now.

He was thrust into the maelstrom of the news cycle last month when he told CNN that the Romney campaign would hit a “reset button” and “like an Etch A Sketch” start with a clean slate for the general election. Rival campaigns and the media pounced.

Those who have followed Fehrnstrom’s career saw it as an exceedingly unusual unforced error.

“That was just so uncharacteristic of him to go off script like that,” a Boston Republican consultant said. “If your coat was on fire, Eric wouldn’t tell you, unless it was in his talking points.”

Fehrnstrom’s Etch A Sketch comment didn’t just affect Romney, it leached into the talking points of Brown’s opponent.

At an event in the Boston neighborhood of Dorchester, Harvard professor Elizabeth Warren, the presumptive Democratic Senate nominee, weaved the popular children’s toy into a speech.

“What the lobbyists want, what Wall Street wants, is they want Etch A Sketch Senators,” she said. “They want the ones who will clear the screen and change their minds to do whatever big money tells them to do. That’s what they want.”