When Speaker John Boehner hired Rebecca Tallent as his immigration adviser, he delivered a clear message that House Republicans are serious about addressing the contentious issue.

Tallent, 34, former chief of staff to Republican John McCain of Arizona, returned to Capitol Hill in December after leaving her post as director of immigration policy at the Bipartisan Policy Center.

Tallent's move set off alarm bells for those who oppose comprehensive reform and earned excited praise from advocates who feared immigration reform was all but dead in the House ahead of the 2014 midterms.

“Hiring Becky sent a very important signal at a very critical time,” said Peggy Ellis, a senior Republican lobbyist representing Esperanza and the U.S. Chamber of Commerce. “This is a reflection of Speaker Boehner wanting to get it done.”

Tallent, a veteran of the immigration debate, has long worked on behalf of comprehensive reform, including a pathway to citizenship for illegal immigrants. Conservatives who oppose such measures as “amnesty” say her return to the Hill makes it inevitable that House GOP leaders will back such proposals.

“She wasn’t hired to twiddle her thumbs,” Bob Dane, spokesman for the Federation for American Immigration Reform, which seeks to limit immigration, told the Washington Examiner. “Tallent is a hardcore, well-connected advocate of amnesty and immigration expansion. No question she was hired by Boehner to get to that goal this year. The table is being set.”

Raised in Tucson, Ariz., Tallent came to Washington after graduating from Carleton College in Minnesota to work for McCain in 2001. She stayed with the senator until 2012, leaving only for a two-year stretch from 2003 to 2005 to work for Rep. Jim Kolbe, R-Ariz., another champion of immigration reform. She joined the Bipartisan Policy Center in February 2013.

Tallent helped McCain write a comprehensive reform bill with the late Sen. Ted Kennedy that provided a pathway to citizenship. It failed to clear a procedural hurdle in June 2007 and was effectively killed, but lawmakers praised her work.

Much of the groundwork she laid was revisited in 2013, this time successfully, when McCain helped pass the bipartisan “Gang of Eight” immigration bill. Some Republicans worry that Tallent, who played a major role in shaping that bill, will push those same measures in the House.

“It makes you a bit uneasy,” Sen. Jeff Sessions, R-Ala., told the Examiner. “It certainly creates the impression that at least some in the leadership of the House are seeking to move closer to the McCain-Schumer Gang of Eight bill.”

McCain dismissed the concerns of those who worry Tallent’s arrival means the House leadership supports “amnesty.”

“That is just foolish,” McCain told the Examiner. “To think she will somehow be driving the speaker’s agenda is insulting to the speaker, because the speaker can think for himself.”

Boehner hired Tallent for one reason, said McCain: “She knows more about the issue than anybody else.”

Under her direction, the Bipartisan Policy Center’s immigration task force produced an August 2013 memo calling for tougher border security coupled with expanded legal immigration and a path to citizenship for those living here illegally.

“Undocumented individuals who pay all penalties, pass a criminal background check and fully comply with other requirements should not be denied the ability to apply for citizenship,” the task force memo reads.

Tallent, through a spokesman for Boehner, declined to be interviewed by the Examiner.

She has expressed her personal views in support of immigration reform in previous interviews and in a November op-ed in the Christian Science Monitor in which she said a comprehensive bill can pass the House only if lawmakers are sold on its merits instead of the politics.

“If advocates and constituents can do that effectively and with a sense of urgency, there is still a chance for reform before the 2014 elections,” Tallent wrote.

In the op-ed, Tallent supported a “piecemeal” approach to reform in the House instead of pushing for a vote on the Senate-passed bill. Her suggestion, made weeks before she returned to the Hill, mirrors Boehner's own roadmap, which calls for debating narrower bills in committee before moving to a floor vote.

Tallent, who lives in Washington with her husband Aaron, is widely admired on both sides of the aisle, and supporters say she is well-equipped to tackle GOP divisions over immigration.

“She’s been doing this for 10 years and she knows the immigration reform substance very well,” said Douglas Holtz-Eakin, who worked with Tallent when he was chief economic adviser to McCain’s 2008 presidential campaign.

“She knows the influential and important outside groups that are going to matter, what the unions and trade groups think, and how the business community is going to react,” he said. “She’s worked in the House, she has worked in the Senate. She has seen what bipartisan reform looks like.”