Senator Marco Rubio’s op-ed in the Wall Street Journal on Friday acknowledged a number of “shortcomings and unintended consequences” in the Gang of Eight’s immigration bill that “need to be addressed.” Rubio specificially cited concerns over the border-security triggers in the bill, as well as the considerable discretion given to the Homeland Security secretary to grant waivers and exemptions.

In response, Senator Jeff Sessions, one of the most outspoken critics of the Gang’s plan, said Friday it “remains to be seen” whether the Gang will allow such improvements to be made via the amendment process. “Marco himself has been more open than any of the other Gang of Eight members to acknowledge there are flaws in [the bill],” Sessions told reporters on a conference call. “He’s [also] been defending the bill, and criticizing those of us who’ve raised questions.”

“The question is: Will the bill’s sponsors, the Gang of Eight, circle the wagons, stick together as they promised to do and defend the bill, or will members actually help us strengthen it?” he added. Other Gang of Eight members, but not Rubio himself, have indicated they are planning to block major amendments to the bill, which is scheduled to be marked up in the Judiciary Committee this week.