One easy way to grasp the challenges facing the Republican Party on immigration reform is to map the political distance between two GOP senators who have been working diligently on the package that the Senate is expected to vote on this week. The problems begin with the fact that they have not been working together.

There’s Jeff Flake of Arizona, a chiseled-faced, 50-year-old freshman whose border-state upbringing made him a natural fit for the “Gang of Eight,” the bipartisan group of senators that drafted the bill under consideration.

And there’s Jeff Sessions, 66, of Alabama, a wily Senate veteran and former federal prosecutor with a thick Southern drawl, who in recent months has devoted his considerable legislative and legal talents to dismantling the bill, bit by bit by bit.

In many ways, the two men represent the two Republican parties that emerged from the GOP’s dismal showing at the polls in 2012: one eager to modernize and grow, the other steadfast in its conservative principles, determined not to be coerced into politically expedient compromise. The side that prevails on immigration will probably be the dominant face of the GOP going into next year’s midterm elections and the 2016 presidential campaign.

Sen. Lindsey O. Graham (R-S.C.), a member of the bipartisan gang, agreed that both senators embody the intraparty struggle on immigration. “What the party’s got to do is have a principled debate,” he said.

Graham called Flake “a value-added” to the Senate’s immigration talks and gave his friend Sessions credit for being “consistent” in his criticism of the effort.

Despite that, Graham said, “I’d go to war with both of them.”

On the immigration bill, the key battle so far is within the GOP.

Flake and Sessions say they share the goal of overhauling the nation’s immigration system with a special concern for fortifying the U.S.-Mexico border. But their visions for that overhaul differ sharply.

“I’ve always felt that if you’re going to be here for 20 or 30 years in a legal status, why not have the possibility and the opportunity and the rights and responsibilities that come with citizenship?” Flake said in a recent interview. “That’s what sets us apart from other countries; it’s a good thing.”

Sessions thinks the current bill is too generous to immigrants who may seek legal status and not aggressive enough on border security.

“We all favor a good immigration reform package. This bill is just not it,” he said Thursday.

Flake needs an immigration bill to pass to meet the expectations of Arizonans who have been living on the front lines of the immigration fight for decades. He must also contend with the political reality of Arizona’s fast-growing Latino population, which has been trending Democratic, partly because of the GOP’s hard-line positions on immigration.

Flake is among those who believe that failure to enact immigration reform could severely handicap the GOP for a long time. With months of complex, closed-door negotiations behind him, he has been walking a fine line, being very careful about making pronouncements on the issue. Since the immigration debate began two weeks ago, he has spoken for only about 20 minutes on the Senate floor.

“You’re expected in the Senate to be seen and not heard for a while, and I’ve tried to respect those traditions,” Flake said.

Sessions, on the other hand, has had the floor for hours. He’s the most vocal member of a group of conservative detractors who see the bill as another huge government intrusion or an attempt by President Obama to reward his political supporters. This group has tried, but failed, to make it more difficult for the nation’s estimated 11 million illegal immigrants to obtain legal status.

Frank Sharry, founder and executive director of America’s Voice, an immigrant rights organization working closely with lawmakers of both parties to enact reform, said Republicans should be wary of Sessions.

“He’s from the hard-core anti-immigrant wing of the Republican Party,” Sharry said. “For smart Republicans who want to modernize the party, he’s their worst nightmare.”

“This is a party that is losing ground with Latino, Asian and immigrant voters, and arguably it cost them the presidency in 2012,” Sharry added. “So when Sessions makes himself the focal point and the face of the Republican Party, it hurts the party.”

On the other hand, Sharry thinks Flake is invaluable: “The fact that he is a border-state senator that has been at ground zero in the immigration wars for much of the past decade makes him potentially quite influential in the Senate debate.”

‘We think we’ve done it’

Flake says he feels a special responsibility on this issue.

Arizonans “expect that if there’s going to be immigration reform talked about and negotiated, you’ve got to be in the middle of it — and that the knowledge that these people have, right on the front lines, is put to use,” he said.

Flake was raised on his family’s ranch in the small town of Snowflake, named for his great-great-grandfather William J. Flake, a Mormon pioneer. At a young age, he worked on the ranch alongside immigrant laborers, many of whom illegally crossed the southern border back and forth to work. Those interactions gave him a deeper, more emotional understanding of how immigrants value the idea of becoming Americans, he said.

“I think we ought to value citizenship, we ought to value the rule of law. There’s a way to do both,” he said. “We think we’ve done it in this bill. The vast majority of Americans out there believe that citizenship ought to be earned and valued, and that’s what we’ve tried to respect in this bill.”

After 12 years in the House, where he worked with Democrats on the issue, Flake came to the Senate in January and launched similar talks with his new colleagues.

He is the most junior member of the closely watched bipartisan gang, and he embraces a much less public role in deference to the national profiles of Graham and Sens. John McCain (R-Ariz.), Marco Rubio (R-Fla.), Charles E. Schumer (D-N.Y.) and Richard J. Durbin (D-Ill.). One senior Senate aide familiar with the talks described Flake as “the high school sophomore hanging out with the seniors.”

His participation has sparked sharp criticism from some of the GOP’s most vocal conservatives, including radio talk-show host Laura Ingraham, who has said she might move to Arizona and run against Flake in a primary because he broke a promise to support more conservative amendments to the immigration bill.

Flake says he understands that some people will never be persuaded to support a bill that would allow the nation’s undocumented immigrants to achieve legal status.

“I think there is a segment of the electorate who just do not believe that anyone here illegally now should ever be able to access a path to citizenship,” he said. “I don’t think that’s a majority position, but it is a deeply held position by a lot of people.”

‘It doesn’t get there’

Jefferson Beauregard Sessions III is one of those people.

The Alabama senator grew up in the tiny town of Hybart, where his father ran a general store. He is the ranking Republican on the Senate Budget Committee but is more at ease discussing immigration policy, a topic closer to his legal roots.

“This bill dramatically increases the flow of immigration, far more than most people realize,” Sessions said in an interview. “The result being, I think, that it does without question endanger job prospects and wages of middle-class Americans.”

“I think legislation is more than [affirming] a vision; that’s sort of what happened with Obamacare — they sold a vision, and people didn’t know what was in the bill,” he said. “Here, they’re selling a vision that people like: ‘We’re going to have the toughest enforcement ever, we’re going to have a legalization process of some kind, we’re going to do a lot of things that people would like to see.’ But when you read the bill, it doesn’t get there. And I’m really baffled why this Senate can’t be crystal-clear that we want a system in the future that’s enforceable.”

As for concerns that his opposition could affect the GOP’s support in the Hispanic community, Sessions suggests the reverse: that the bill is “not in the national interest for millions of Hispanics who are working today.”

“We welcome somebody here . . . implicitly we’re saying, ‘We’re going to create an environment where you have a chance to be successful.’ And if you create an environment that isn’t successful, isn’t that hurting minorities? Isn’t that hurting immigrants, isn’t it hurting Hispanics? I think it is,” he said.

Months of careful bipartisan negotiations are likely to result in final passage of the immigration bill in the coming days — and Sessions plans to keep speaking out until then.

“I think this bill should be defeated; I do not believe it should pass in its present form,” he said. “I think it’s really important for the American people to know that it’s flawed, and I intend to do my best and then we’ll vote. . . . I think that as they find out more about it, support will erode.”