Republicans critical of US-Iran nuclear talks contend President Barack Obama is so keen for a deal that he is ignoring Tehran's moves to expand its influence across the Middle East.
Republican hawks maintain that Obama wants so much to burnish his legacy by negotiating an agreement to restrain Iran from becoming a nuclear-armed state that he is not pushing back against Iranian activities in Iraq, Yemen, Syria, Lebanon and Bahrain.
Secretary of State John Kerry has taken on lawmakers, including some who insist that the nuclear negotiations have hamstrung US policy decisions in the region.
"Yes, Iran's influence has spread at this moment and we are deeply concerned about it," Kerry said at one congressional hearing. "But if you're concerned about it now, think of what happens ... if they had a nuclear weapon."
Republicans point to the activities of Iran, the dominant Shiite force in the Middle East, in these countries:
Iraq: Iran-backed militias are fighting alongside Iraqi forces to retake Tikrit, a Sunni stronghold seized by Islamic State militants. Army Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, says the US worries that the militiamen, who are Shiite, eventually might turn against Sunni and Kurdish Iraqis, further destabilizing the country.
Yemen: The Obama administration had cited Yemen as a success in the fight against terrorism. But Houthi rebels, backed by Iran, seized the capital, Sanaa, from a US-backed leader who supported American drone strikes against suspected al-Qaeda figures. Nick Rasmussen, who directs the National Counter Terrorism Center, recently told the Senate Intelligence Committee that Yemen's American-funded army failed to oppose advancing Houthi rebels, and that the government's collapse surprised the US.
Syria: Iran supports Syrian President Bashar Assad, who has waged an unrelenting campaign of bloodshed and starvation against his own people for years and is fighting against moderates trying to topple him. On the military front, Tehran has provided advisers and billions of dollars in aid and has roped in Shiite militias from across the region, particularly Lebanon's Hezbollah but also fighters from Iraq, to reinforce Assad's troops.
Lebanon: Iran's link to Lebanon is through its decades-long support for Hezbollah, Lebanon's Shiite militant group.
Bahrain: Bahrain, which hosts the US Navy's 5th Fleet, is led by a Sunni monarchy that has struggled to quell Shiite protests demanding greater rights and equal treatment. Leaders in Bahrain claim Iran is helping Shiite militias; Iranian leaders accuse leaders in Bahrain's capital of supporting anti-Iranian forces there.
"The Iranians are now in Sanaa. They're in Baghdad and Beirut and Damascus and meanwhile this president and secretary of state pursue the mirage of a nuclear agreement," Republican Sen. John McCain, the chairman of the Armed Services Committee, said in a recent speech.
Directing the offensive in Tikrit is Iranian Gen. Qassem Soleimani, commander of Iran's powerful Revolutionary Guard's Quds Force. The overt Iranian role and the prominence of Shiite militias in the campaign have raised fears of possible sectarian cleansing should the city fall.
Republican Sen. Lindsey Graham complained that the administration remains silent about the havoc Iran is creating on the ground.
"If I were president, I would tell the Iranians we're not going to talk to you any more about your nuclear ambitions until you stop destabilizing the region and invading your neighbors," said Graham, who is weighing a presidential bid.
Among the Democrats countering the Republican refrain, Sen. Tim Kaine says he shares the concern about Iran's involvement but "this is not about turning Iran from an enemy into a friend. This is whether an enemy has a nuclear weapon or doesn't. The administration is very realistic. If there is a good nuclear deal, we still have to confront the adventurism of Iran beyond its borders."
Late last year, Obama designated the six-member Gulf Cooperation Council as eligible for foreign military sales, meaning they can purchase weapons as an entity in order to lay the groundwork for them to deal with challenges that they feel from Iran.