The Senate will begin a historic debate today that could overhaul the nation’s immigration system.

Senators will get their first crack at modifying or killing legislation that a bipartisan group of eight colleagues proposed last month.

The so-called Gang of Eight introduced the 844-page measure in hopes of offering a long-elusive solution to the immigration problems that have plagued the nation for decades. It’s the first real effort in six years.

The road ahead is full of political peril.

The contents of the 300 proposed amendments illustrate the difficult path ahead. The proposals range from an attempt to speed the path to citizenship for the youngest here illegally to an effort to make it nearly impossible for most others to become citizens.

One measure, known as the “Little Dreamers” amendment, would eliminate provisions that deny younger children a five-year path to citizenship available to many of their older siblings.

“It’s very arbitrary,” said Wendy Cervantes, who heads immigration work for the children’s advocacy group First Focus, “because the idea is those who enter as children should have a faster pathway to citizenship.”

The leading opponent of the immigration overhaul, Alabama Republican Sen. Jeff Sessions, introduced nearly 50 amendments that, among other things, limit the number of people who may gain legal status, block guest-worker visas if the unemployment rate is above 5 percent and require stricter border-enforcement measures before legal status is granted.

“The Gang of Eight plan fails to live up to every major promise of its sponsors,” Sessions said.

The question is whether the Gang of Eight can hold together and withstand an onslaught of efforts to blow up its pact.

The Senate Judiciary Committee, which will begin considering amendments today, includes four members of the group, Democrats Charles Schumer of New York and Richard Durbin of Illinois, and Republicans Lindsey Graham of South Carolina and Jeff Flake of Arizona.

Group members said they’d protect the core aspects of their bipartisan plan and fight so-called “poison pill” amendments intended to break the coalition. But team leaders Schumer and John McCain, R-Ariz., have said they’re open to considering amendments that all agree will improve the bill. Florida Sen. Marco Rubio, a Republican leader of the group who isn’t on the Judiciary Committee, has said the bill must be strengthened in order to receive Senate approval.

Conservative supporters of overhauling immigration see adding same-sex benefits as the next poison pill that might break up the tenuous pact.

Senate Judiciary Committee Chairman Patrick Leahy, D-Vt., introduced an amendment that would permit citizens to sponsor same-sex “permanent partners” who are applying for legal residency.

“For immigration reform to be truly comprehensive, it must include protections for all families,” Leahy said in a statement. “We must end the discrimination that gay and lesbian families face in our immigration law.”

Schumer had urged that same-sex benefits be in the immigration package, but Republican members threatened to walk away if they were. Graham, Rubio and McCain have said the measure might derail the entire package.

Conservative supporters, such as Roman Catholics and evangelicals, also have warned that they might pull their support if same-sex benefits are in the package.