With one hearing down, another in full swing Monday and one more to go, the Senate Judiciary Committee is the first crucible for a comprehensive immigration overhaul bill. And in that cauldron will be the heat-bringing Republicans who likely will do everything in their power to stop the legislation from passing, trying to puncture holes in a delicate agreement forged by a bipartisan group of eight senators.

Only two of the four “gang of eight” Republicans serve on the Judiciary panel, and Sens. Lindsey Graham, R-S.C., and Jeff Flake, R-Ariz., are far outnumbered by GOP detractors on the committee.

So who will have the harshest words about the bill in the hearings and expected May markup? These guys:

Sen. Jeff Sessions, R-Ala.

Sessions is known for an aggressive press operation that often blasts out multiple releases a day, mostly under the Republican’s purview as ranking member of the Senate Budget Committee. Between April 17 and April 19, Sessions sent out 11 releases or advisories slamming the bipartisan immigration bill. He and Sen. David Vitter, R-La., held a dueling news conference on April 18, as the gang of eight was addressing the media.

“You have not gotten the full story, or correct story, on this issue. Today you will hear the alarming facts, straight from the source,” Sessions told reporters as his counterparts unveiled their sweeping legislation. “No immigration bill should ever pass Congress that the law enforcement officers on the ground tell us won’t work or can’t be enforced.”

Incidentally, Vitter, who is not on the Judiciary panel, ran an anti-immigration ad during his 2010 re-election bid that was slammed at the time as “racist.”

Sen. Charles E. Grassley, R-Iowa

Grassley made the most news at the Judiciary panel’s first hearing last week, when he explicitly linked the Boston Marathon bombings to immigration.

“We also appreciate the opportunity to talk about immigration. Particularly in light of all that’s happening in Massachusetts right now and over the last week,” said Grassley, who is the panel’s ranking member. “We are here trying to understand why these events have occurred. … It’s hard to understand that there are people in this world that want to do Americans harm, so this hearing is an opportunity to refocus on the issues at hand and the importance of remaining vigilant and secure in our homeland.”

The Iowa Republican is not traditionally considered part of the conservative tea party bloc that could cause the most trouble for the bill, but he sure upset gang of eight members by suggesting a link between the terrorism in Massachusetts and the nation’s immigration system.

Sen. Ted Cruz, R-Texas

Cruz, a freshman from Texas, has in a few short months established a reputation as a member who is not afraid to stir the pot in committee hearings. He has attacked President Barack Obama’s cabinet nominees during confirmation hearings. And he once so enraged Democratic Sen. Dianne Feinstein of California during a Judiciary session on her assault weapons ban that she lashed out at him for what she deemed a condescending tone: “I’m not a sixth-grader,” she said at the March committee meeting. “I’m reasonably well-educated, and thank you for the lecture.”

Also of note is that his in-state colleague, No. 2 Senate Republican John Cornyn, has voted with Cruz on multiple occasions, even when it’s been highly unpopular. Cruz and Cornyn were two of only three senators to vote against the confirmation of John Kerry to secretary of State. Cruz also was one of the most outspoken opponents of a bipartisan bill to expand the nation’s background checks last week.

Sen. Mike Lee, R-Utah

Lee, swept into Congress by the GOP wave of 2010, is one of the Senate’s tea party stalwarts. Though there are at least two hearings in the coming weeks, Lee’s remarks on April 19 were less adversarial in tone, and he focused primarily on concerns with procedure.

“There is no way that we as a committee could possibly be prepared this morning to debate more than a fraction of this massive bill. It would be impossible to have a meaningful discussion with rigorous analysis under such circumstances,” Lee said. “Witnesses were asked to submit written testimony before they could have conceivably read the entire bill. And even with the help of committed staff who have worked through the night in preparation, none of us can honestly say that we understand each provision or how all the pieces fit together. Not even close.”

Republicans are expected to use a process-based argument against the bill, which is likely why Sen. Marco Rubio, R-Fla., a member of the gang of eight and a heralded conservative of the class of 2010, has pushed for multiple hearings and regular order in considering the legislation.