The member of Iowa’s Congressional delegation with the most influence in the current immigration debate isn’t the outspoken Republican Rep. Steve King, who on Tuesday said at a press conference that he would sooner support “Obamacare” than the Senate bill he called an “amnesty plan.” No, it’s another Republican — Sen. Chuck Grassley.

The Gang of Eight immigration bill — so named for the bipartisan group of eight senators who cooked up the legislation — was sent to be refined in the Senate Judiciary Committee, on which Grassley is the ranking Republican member. The Judiciary Committee is tasked with adding amendments to the bill that can range from minute changes to major policy alterations.

When this mark-up process is done, the committee will report out the bill, meaning that it will be available for the full Senate to consider if the senators so choose.

The original Gang of Eight immigration proposal included measures that would offer a path to citizenship for many of the nation’s 11 million unauthorized immigrants, tighten border security, establish a strict employment-verification system, and expand the current legal immigration system to bring in more high- and low-skill workers.

As the ranking minority member of the committee charged with tweaking the immigration bill, Grassley has a lot of power to alter it as he sees fit. Only two days into the revision process, he has made his mark on the bill.

So far, Grassley’s contribution to the bill has been mostly positive. One Grassley amendment expanded border-security strategies to include all points along the border, not just high-risk areas as the original bill specified.

Considering the historical border-security precedents, this may prove to be an important detail. Past efforts at securing high-risk areas have had the effect of simply creating new high-risk areas in spots with fewer border-control resources. More evenly distributing these resources could stop such a phenomenon from occurring.

Another successful Grassley amendment instituted a mandatory audit of the Comprehensive Immigration Reform Trust Fund, the immigration bill’s funding pool, which will include money allocated from Congress’s general fund as well as some fees collected from immigrants applying for legal status. In a deficit-conscious Congress, Grassley’s provision to require stricter financial reporting could improve the political viability and long-term budgetary outlook of the bill.

But not all of the changes Grassley has offered have been positive. One such proposal that was struck down 12-6 in the committee would have prohibited the government from giving immigrants provisional legal status until “effective control of the borders” had been maintained for six months.

This proposal would have effectively tied the important first step in the path to citizenship to increased border security, a goal that has been difficult to accomplish in the past even with massive resource deployments.

Grassley was disappointed that his enforcement amendment failed.

“… without approval of provisions like my amendment to ensure the border is secure before undocumented immigrants are legalized,” Grassley said after the first day of mark-up, “it’s clear … that it’s legalization first and enforcement later.”

As the Judiciary Committee continues to mark-up the immigration bill, Grassley will have a lot of power to shape an important policy. We urge the senator to act sensibly and in good faith to move responsible, much-needed immigration reform to a vote in the Senate.