WASHINGTON When a bipartisan group of U.S. senators began writing legislation to overhaul the nation's immigration laws in January, many Republican leaders embraced the effort as a savvy strategy for fixing the party's tattered image with Hispanic voters.
But since the bill was rolled out last week, a rift has emerged among conservatives that has played out in Senate hearings on Capitol Hill, on conservative talk shows and in social media such as Twitter and blogs.
The immigration effort has brought together an unusual coalition of Republicans, led by Florida Senator Marco Rubio, a potential 2016 presidential prospect, Arizona Senator John McCain, a former presidential candidate who has broken ranks with his party on some issues, and conservative anti-tax activist Grover Norquist.
But it has also put a spotlight on longstanding opposition to immigration reform within the party, potentially blunting the message party leaders had hoped to send in their efforts to remake the party's image, begun in earnest by the Republican National Committee after President Barack Obama swept to victory with 71 percent of the Hispanic vote in 2012.
Opponents of immigration reform include some traditional conservatives such as Senator Jeff Sessions of Alabama as well as some relative newcomers, including Texas Senator Ted Cruz, a Tea Party favorite. Another opponent of the immigration reform bill is Jim DeMint, a former South Carolina senator who is now president of the Heritage Foundation, a conservative think tank.
Luke Frans, executive director of Resurgent Republic, an organization that conducts polling and research for Republicans, said his group has met with Capitol Hill Republicans on the subject, advising them to avoid allowing the debate over immigration to become a "circular firing squad" in which Republicans are attacking their own.
"Conservatives have certainly seen in past debates where it's veered off the policy and become more of a personal tone. That's what we're really trying to avoid this time around," he said.
Critics of the legislation have labeled as "amnesty" a provision at the heart of the bill that would grant legal status to millions of undocumented immigrants. They also warn that the legislation would drive up the federal debt as immigrants eventually become eligible for federal benefits such as Social Security.
Supporters say providing legal status for the undocumented would bring people out of the shadows and ensure that they are working and paying taxes. Advocates also say the bill, which would establish new guest worker programs for both highly skilled and low-skilled workers, would boost the economy by making the labor market more flexible.
The debate is still in its early stages and many Republicans say the rancor is still far from the level that it reached in past immigration debates, such as one in 2006 and 2007 when criticism of comprehensive immigration reform on talk radio jammed phone lines at the Capitol.
But it may not be far beneath the surface either, to judge from some of the exchanges in the past week.
In a posting that highlighted the divisions among conservatives, Erick Erickson of the influential RedState political blog accused Rubio staffers and other supporters of the immigration bill of trying to paint critics as bigoted and racist.
Elsewhere, especially on Twitter, some conservative opponents of the immigration bill accused Rubio - falsely - of supporting the distribution of free phones to illegal immigrants.
Rubio has spent much of the last week appearing on conservative radio and TV stations to defend the legislation.
"We always realized that this was a complicated issue and that we were going to have to spend a lot of time explaining it," Rubio spokesman Alex Conant said. Conant described the response so far in conservative media as "mixed."
The bomb attack at the Boston Marathon last week that was allegedly carried out by two immigrant brothers of Chechen descent intensified the debate among Republicans over the immigration bill.
Some Republicans, including Senator Charles Grassley of Iowa and Senator Rand Paul of Kentucky, said the Boston attack, which killed three people and injured more than 250, were a reason to be cautious on immigration reform.
But other Republicans, including House of Representatives Speaker John Boehner and House Budget Committee Chairman Paul Ryan, argued that the Boston bombing showed the need to fix and modernize the immigration system.
While DeMint of the Heritage Foundation has been a vocal skeptic of the immigration reform bill, many of the scholars at two other influential conservative research organizations, the Cato Institute and the American Enterprise Institute, have been supportive of broad reform.
Charlie Black, a longtime adviser to Republican candidates who is now chairman of Prime Policy Group, a public affairs consulting firm, said the divisions among Republicans do not break down "along traditional lines" of conservative and moderate.
Whit Ayres, a Republican strategist who backs immigration reform, said Republican voters who may be skeptical of the effort are persuadable if proponents use the right message on immigration reform.
He said the strongest argument is that the current immigration system amounts to a "de facto amnesty" and that reforming the system is "better than anything (Democratic President) Barack Obama, left to his own devices, is likely to come up with."
Some conservative activists may be easier to persuade than others on immigration reform.
Chris Littleton of the Tea Party group Ohio Rising, said he did not understand what was behind all of the criticism of immigration reform.
"There are clearly employers who need low-cost labor and immigrants who want jobs, so there is clearly a functioning market here. Everybody's benefiting from the situation so I don't know why we need this debate," he said.
But David Crow of the Arkansas Conservative Caucus, another Tea Party group, said the proposed immigration bill would "simply create a magnet for more and more people to come across the border."
"In my opinion it is a huge mistake to go down this path when it's evident it will attract more and more illegal aliens," Crow added
(This story is refiled to correct reference to Chechen brothers in 16th paragraph)
(Additional reporting by Nick Carey; Editing by Fred Barbash and Lisa Shumaker)