When House Majority Leader Eric Cantor lost his Republican primary last night, pundits were left asking how his potential departure from Congress would affect GOP moves on policy matters like immigration, where the Virginia Republican had sometimes played a moderating role. But few discussed another policy area where Cantor exerted influence: on Middle East issues, particularly on today's hot button of Iran.

Some activists on Capitol Hill noted Cantor's role marshaling support for aggressive measures on Iran. "No one in the House Republican Leadership takes as hawkish a position on Iran as Cantor does," one Hill activist working on foreign policy said. "On this issue, he really pushed the Leadership and folks ceded control of the issue to him."

Cantor has long been a vocal Congressional hardliner on Iran, and an opponent of the Obama administration's diplomacy with the Islamic Republic.

A former Democratic national security aide on Capitol Hill said, "[House Speaker John] Boehner has in essence delegated GOP foreign policy to Cantor, and now he's gone." The aide added that Cantor spoke with "sophistication and understanding on the issue, and aggressiveness."

The Hill activist pointed to Cantor's close relationship with AIPAC, the powerhouse pro-Israel lobby group that has been skeptical on diplomacy with Iran and pressed a tack that critics fear could endanger prospects for a comprehensive nuclear deal being negotiated with Iran.

"As the lone Jewish Republican, he was the Republican point person with AIPAC and the broader Jewish donor world," the activist said.

A current Congressional aide concurred: "AIPAC had no better friend in the House than Eric Cantor. I don't think it's an overstatement to say he deferred to whatever they want." The aide pointed to Cantor leading trips to Israel in concert with AIPAC's education arm for new Republican members of Congress.

But the aide cautioned that Cantor's departure may not have a momentous effect. "I actually don't think it's going to have significant ramifications," the aide said. "AIPAC's probably freaking out right now because they lost their number one guy in the House, but it's just going to take a little bit of more relationship building for them."

The Hill activist, however, pointed to Cantor's sometime cooperation with Democratic Minority Whip Steny Hoyer (MD) on Iran issues. "It was the constant pressure from Cantor that Hoyer frequently felt he had to respond to regarding Iran legislation and letters," the activist said.

In December, Cantor initiated work on a resolution that would have called for any final deal with Iran to bar the Islamic Republic from any enrichment of nuclear fissile material—a condition, often pushed by Iran hawks, that many experts view as a non-starter in talks. But Hoyer, who at first cooperated with the effort, backed out at the last minute under pressure from the Obama administration.

In March, Hoyer and Cantor reunited on a letter that the Congressional aide described as "so milquetoast that even J Street"—the liberal pro-Israel group—"endorsed it, which I'm sure pissed off AIPAC." The letter did not contain a demand that Iran end all enrichment. Hoyer may be better enabled to make pushes such as his moderating efforts on the failed resolution and the subsequent letter.

The former national security aide said that AIPAC's role and Iran issues were only part of a larger story. "There's no one that's going to be hostile to AIPAC's interests," they said. But, "what's going to happen to House GOP foreign policy with Cantor leaving?"

Looking at Cantor's potential replacements as Majority Leader, it was unlikely any would take the care Cantor did with foreign policy issues, said the former Democratic aide, who feared the GOP may even slip into neo-isolationism. "Eric Cantor was an adult in the room on foreign policy," they conceded. "As a partisan, it's nice to see a GOP totem pole fall, but it's kind of shitty for the country."